April 30 2014 1:00 PM

Day of the Exoplanet

By Phil Plait

That bright dot? Yeah, that's an entire alien planet, seen directly in this photograph. And now we know how long its day is.

Photo processing by Christian Marois, NRC Canada

For the first time, astronomers have determined how fast an exoplanet is spinning. To save you the dramatic tension, I’ll tell you right off the bat: 25 kilometers per second, or about 28,000 mph. That’s fast. With some reasonable assumptions, that means the planet has a day that’s about eight hours long, a third of an Earth day, which is pretty amazing given that the planet is 10 times the mass of Jupiter!

The planet in question is Beta Pic b, a massive gas giant orbiting a star about 63 light years away. The planet was discovered in 2003, and its existence confirmed in 2009. This planet has been a boon to astronomers; it was one of the very first to have been directly imaged by telescopes, meaning we can actually see it in pictures. The image above shows it clearly near its parent star, Beta Pic.

Not only that, but over time we’ve seen it physically move around its star. That tells us its orbital period (its year) is 17-20 Earth years long. While getting the year of the planet was quite a treat, getting the length of its day is substantially harder. To do this, astronomers took advantage of the Doppler shift, the same effect that changes the pitch (the wavelength of the sound) of a motorcycle as it passes you (the familiar “EEEEEEEE-yowwwwwww” sound). When the motorcycle approaches you, the pitch is higher, and when it moves away the pitch drops.

The same thing happens with light: If a source approaches you the wavelength changes, shifting toward shorter wavelengths (what astronomers call the blue end of the spectrum, so we call this blueshifting). If it’s heading away, the wavelength of light gets longer (redshifting). If the source is moving quickly enough, this can be measured.

The astronomers used a spectrograph, a device that breaks up light into thousands of individual colors (called a spectrum), to observe Beta Pic b. The atmosphere of the planet has some carbon monoxide in it, and that molecule absorbs light at a very specific wavelength. It’s like a filter that blocks the light at a narrowly defined color, making a dark line in the spectrum. This is useful, because as the planet moves, the wavelength of the absorption line in the spectrum changes due to the Doppler shift. That’s what astronomers used to tag the velocity of the planet.

The visible light spectrum of the Sun shows dark absorption lines, where various elements (like hydrogen, calcium, and so on) absorb light at specific colors, essentially blocking those colors from leaving the Sun.

Photo by N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF

The CO absorption dip they found for Beta Pic b was blueshifted by about -15 km/sec (the minus sign indicates velocity toward us). That’s just what you’d expect for a planet at that distance from its parent star in a circular orbit. So right away, they could measure the orbital speed of the planet.

But there’s more. Since CO absorbs light at a specific color, you’d expect to see a sharp drop in the spectrum. But that’s not what they saw! Instead, the dip is broadened, smeared out. That, it turns out, is the key to its rotation.

Imagine a spinning ball. When you look at it, the left side (say) is spinning toward you, and the right side spinning away. If you could very carefully measure the light from it, the left side would be blueshifted, and the right side redshifted. The light from the middle wouldn’t be shifted at all. So you’d see velocities ranging from the maximum blueshift, through zero, out to the maximum redshift. The profile you’d see would be smeared out … just like that of Beta Pic b.

When they measured how broad the absorption profile of CO was, they found it must be spinning with a velocity of about 25 km/sec. If you were standing (or really, floating) on the planet’s equator, you’d be moving at 90,000 kph (56,000 mph)!

To get the length of the day you have to figure out how big the planet is. For example, the Earth spins at 1,700 kph, and has a radius of 6,371 km. That means its day is 24 hours long, give or take (I’ll leave that math as an exercise for the reader, but remember the circumference of a circle is twice the radius times pi).

We don’t really know how big Beta Pic b is, but theoretical models give it a radius of about 1.65 times that of Jupiter, or 115,000 km. Given the velocity measured, that means its day would last a mere eight hours. Imagine: This is a planet 18 times wider than Earth, yet spinning so rapidly its day is a third as long!

Actually, this fits with what we know: In our solar system, the bigger the planet, the faster it spins. We think that’s left over from when the planets formed billions of years ago from the disk of material around the Sun. As bits and pieces coalesced to form the planets, their rate of spin increased, just like water in a sink speeds up as it approaches and spins down the drain. Planets that are bigger had more material fall in, so they sped up more then smaller planets.

And Beta Pic b isn’t done yet. It’s very young, only a dozen or so million years old, and young planets are hot. Since it’s mostly gas, that means as it ages it will cool and shrink. That will spin it up even faster, like an ice skater spins faster when she brings her arms in. In a few hundred million years, Beta Pic b may have a day only three hours long.

You think there’s not enough time in a day now to get anything done. It could be way worse. Imagine a three-hour day!

An artist's impression of Beta Pic b. Note that it's depicted as oblate. Click to spheroidenate.

Drawing by ESO L. Calçada/N. Risinger

If it’s spinning that rapidly, Beta Pic b must be really oblate, oval shaped (Saturn and Jupiter are noticeably noncircular due to their rapid spins). And it’ll get even wider at its equator as it ages. Hmmm … if there’s a metaphor there I may be missing it.

All of this is astonishing to me. Twenty years ago we didn’t even know if there were planets orbiting Sun-like stars at all. Now we know of 1,700 and counting. We’ve directly photographed a dozen or so of them. And this one, Beta Pic b, we’ve seen moving around its star. We know a bit about what’s in its atmosphere (carbon monoxide), we know its orbital speed, and have now measured its spin and inferred the length of its day! And mind you, we’ve learned all that from more than 600 trillion kilometers away.

If anyone tells you science isn’t cool, you now have one more arrow in your quiver to rebut them. Science is cool. Astronomers take the measure of the Universe by the starlight that falls to Earth, and discover what things are like on alien worlds. That’s about the coolest thing there is.

The entire universe in blog form

April 29 2014 7:30 AM

You Light Up My Gas

By Phil Plait

Star formation is a seriously gorgeous business. Just look at Gum 41!

That picture above is from the European Southern Observatory’s MPG/ESO 2.2-meter telescope in Chile (wanna see the ginormous 4,000 x 4,000 pixel version? Yes. Yes, you do.). It used filters that more or less mimic what the eye sees, with an added filter that only lets through the light of warm hydrogen gas—that’s the pervasive red glow in the nebula.

Gas like that is a pretty good sign that somewhere nearby, stars are being born … and it’s hard to miss that blue one right in the center of the roughly circular nebula. That star is called HD 100099, and it’s actually two stars in a tight orbit (far too small to be separated on the scale of this picture). Both stars are monster O-types, meaning they are far, far more massive than the Sun, far hotter, and ridiculously brighter. Either one would be enough to light up the gas around it, but both together blast the gas with vast amounts of ultraviolet light. This heats the gas up, exiting the atoms in it, which respond by glowing with that characteristic and quite lovely red hue.

What results is a classic shape called a Strömgren sphere, named after the astronomer who worked out its physics. The overall shape is roughly spherical, because the edge is defined where the light from the central stars weakens enough that it can no longer excite the gas. There is gas outside that region, but it’s not lit up so we can’t see it.

Not only that, but both stars blow out a fierce wind of subatomic particles, like the solar wind but much more powerful. This carves a cavity in the center of the gas, an expanding bubble snowplowing the material outside it. If you look more closely at the center region you see bright ridges where the wind slams into the surrounding gas, compressing it and making it glow even more brightly:

Photo by ESO

Together, these processes give this cloud a shape something like a flower, but one a dozen light years across and thousands of light years away.

Do you see the 50-light-year-high running chicken?

Photo by Marco Lorenzi, used by permission

The nebula was discovered by astronomer Colin Gum (hence the name) and is part of a much larger complex of star-forming gas called IC 2944, also called the Running Chicken Nebula, due to an apparently drug-induced interpretation of the shape looking like the jogging fowl. Interestingly, I thought it was part of the foot, but I’ve seen others say it’s the chicken’s wingtip. I suppose Gallus domesticus is in the eye of the beholder.

Anyway, as you can see, the whole region is littered with glowing gas. It takes massive, hot stars to excite gas like that, and those kinds of stars don’t live very long—a few million years at most. Compare that to the 4.6 billion year age of the Sun and you can see why we call them “young.” And that’s how we know to look for red gas when we want to find stellar nurseries! They’re like neon signs (literally) pointing us to the youngest stars in the galaxy. If you’re looking for amazing science, big red nebulae are what you can look for.

And if you’re looking for beauty, it’s the same. But that’s true for so much of astronomy, and one of the many reasons I love it.

Related Posts

Jaw-Dropping Rotating 3-D Nebula (Yeah, you wanna click that)
An Ionized Rose Would Smell as Sweet
Rudolph the Red-Nosed Strömgren Sphere

April 19 2014 7:30 AM

That’s No Moon… Well, Actually, Yeah It Is

By Phil Plait

Now witness the firepower of this fully armed and operational lunar ranging station! Click to midichlorianate.

Photo by Tom Murphy, used by permission

So there’s a picture you don’t see every day. Clearly, Vader’s forces were not at all happy about the lunar eclipse.

I know, it really does look like the Moon was shooting out a laser at a passing ship, but that’s an illusion: in fact, that laser is hitting the Moon, and it was sent from Earth.

While you and I were busy watching the total lunar eclipse on Monday, a bunch of astronomers were zapping it with high-powered lasers. They do this every now and again to find to exactly how far away the Moon is (and to provide yet another test of relativity).

Apollo astronauts left a series of retroreflectors there, devices that are designed to reflect light back in exactly the same path it came in. If you shoot a retroreflector with a laser, the beam will come back directly at you. Over the course of 800,000 km (500,000 miles) to the Moon and back the beam spreads out a lot, so a telescope is used to collect the photons from the laser.

Since we know the speed of light very accurately, the time it takes for the beam to hit the Moon and come back tells us its distance. Think of it this way: If you are traveling at exactly 100 kph, and you drive for exactly one hour, you know you drove 100 km. Same thing here, but the car is a photon, the speed is the speed of light, and the distance is a wee bit more then you’d go for a family outing.

In this case, the retroreflector was left by the Apollo 15 team. I knew this right away! How? Because this:

Close-up of the laser shot (left) compared to a map of the Moon showing the Apollo 15 landing site (right; Apollo 17 is also listed).

Photo by Tom Murphy; Soerfm/wikipedia

Apollo 15 landed on the very eastern edge of Mare Imbrium (the large dark circle; actually a lava plain), near the border with Mare Serenitatis. As you can see, the beam converges right at the Apollo 15 spot. I know it looks like the beam is coming from there, but that’s perspective for you! The beam appears to get smaller with distance, and your eye can’t tell if it’s getting smaller as it heads away, or getting bigger as it comes closer.

Astronomers have been measuring the Moon’s distance for many years, and it’s from that we’ve learned the Moon is moving away from the Earth by about 4 centimeters per year due to the complicated interaction with Earth’s gravity. But today I learned something about this: During a full Moon, the amount of light reflected back from the Moon drops. This was a mystery for quite some time, but it turns out that’s due to the way the mirrors there are set up; the Sun shines down them and heats them up, and they lose their efficiency at reflecting light back to us. During an eclipse, though, the Earth blocks the Sun during the full Moon, so the mirrors don’t heat up. They reflect light back to us just fine, proving that solar heating was the problem.

It’s funny to think that while I was collecting photons to make photos and video of the Moon, astronomers a thousand kilometers south of me were sending photons to the Moon… and getting them back.

Tip o’ the X-Wing to Tom Murphy for letting me use his photo, and to APOD, where I first saw it. I'll note this is at least the fourth time I've used a variation of this headline, and it's funny every flippin' time.

The entire universe in blog form

April 17 2014 2:09 PM

An Astronomical Discovery: Earth-Size Planet Found in Its Star’s Habitable Zone

By Phil Plait

Artwork depicting the newly discovered Earth-size planet Kepler-186f and its sister planets. Click to embiggen, and you really want to; this is a pretty stunning piece of artwork.

Drawing by NASA Ames/SETI Institute/JPL-CalTech

I have some cautiously exciting exoplanets news: Astronomers have announced the discovery of a planet that is very nearly the same size as Earth and orbiting its star in the habitable zone—that is, at the right distance from its star to have liquid water on its surface. We don’t know how Earth-like it is, but this shows that we’re edging closer and closer to finding another Earth, and this one is the best bet we’ve found so far.

The planet is called Kepler-186f and was discovered using the Kepler Space Telescope, which was designed to look for planets orbiting other stars. Kepler exploits what’s called the transit method: It stares at 150,000 stars all the time, looking for dips in the amount of light received from every star. The idea is that if a star has planets, and if we see the orbits edge-on, then every time the planet passes between us and its parent star it’ll block an teensy bit of light (usually far less than 1 percent).

This method is extremely powerful—about a thousand planets have been found this way in Kepler data! In fact, most of the planets found this way have been from Kepler. Another cool thing is that if you know how big the star is (and we generally do) then you can also determine the size of the planet by how much light it blocks.

Kepler-186f is one of the big success stories. It’s part of a mini-solar system, a five-planet system orbiting a red dwarf: a smaller, cooler star than the Sun. The other four planets (Kepler-186b-e) are all very roughly Earth-size, but orbit far closer to the star, ranging from 5.1 million kilometers (3.2 million miles) to 16.5 million kilometers (10 million miles)—for comparison, Mercury orbits the Sun at a distance of about 50 million kilometers (31 million miles), so this really is a solar system shrunk down. But even though the star is cooler than the Sun, these planets are close enough to it to be pretty hot; even the farthest of the four previously known would be hot enough to boil water on its surface (assuming it has a surface).

Worlds alike: a comparison of the sizes of Earth and Kepler-186f.

Drawing by NASA Ames/SETI Institute/JPL-CalTech

186f is different, though: It orbits farther out, about 53 million kilometers (33 million miles) from the star, where temperatures are more clement. Making some basic assumptions, it lies near the outside edge of the star’s “habitable zone,” where liquid water can easily exist on the surface of a planet. We know of several dozen planets like that in the galaxy so far, but what makes 186f special is its size: it’s only about 1.1 times the size of Earth! Together, these make it potentially the most Earth-like planet we’ve yet found.

I say potentially because honestly we don’t know all that much about it besides its size and distance from its star (and its year—it takes 130 days to orbit the star once). The next things we’d need to know about it are the mass, what its atmosphere is like, and the surface temperature. The gravity of the planet depends on its mass, and in many ways the atmosphere depends on the gravity.

Unfortunately, we don’t know either, and we’re unlikely to. The techniques used to find planet masses aren’t up to the task for this planet—the star is too dim to get reliable data. The same is true for any air the planet might have as well. And without that, we don’t really know its surface temperature.

So we don’t know if this planet is like Earth, or more like Venus (with an incredibly thick, poisonous atmosphere that keeps the surface ridiculously hot), or like Mars (with very little air, making it cold). It could be a barren rock, or a fecund water world, or made entirely of Styrofoam peanuts, or some weird thing we haven’t even imagined yet.

Still, our models of how planets form are getting better, and we’re getting a handle on how they behave. According to what we know, it’s most likely that Kepler-186f is a rocky planet like the Earth, with a similar surface gravity. That in turn implies it could have water. But again, we just don’t know, and anything beyond this is speculation; there are a lot of factors in making a planet habitable. As a random one, it may take a magnetic field to make a planet livable. Ours protects us from the constant stream of subatomic particles the Sun emits, which, over several billion years, would have eroded away Earth’s atmosphere. That may be what happened to Mars.

To be fair, I’ll note that there is one planet found before that’s roughly the size of Earth (though bigger than Kepler-186f) and in its star’s habitable zone, but in that case the planet orbits at a distance where it receives about as much heat and light from its star as Venus does from the Sun … and look where that got Venus. Kepler-186f is therefore more likely to be Earth-like than that other planet, though again we can’t be sure with the information we have now.

Still, this is exciting news—after all, one of the main mission objectives of Kepler was to do just this: find an Earth-sized planet in its star’s habitable zone. So, my congrats to the team of astronomers involved: It’s very nice indeed to see a spacecraft achieve its goal! And there’s still lots and lots of data to go through from Kepler. There could easily be many, many more such worlds hidden in the blips of starlight Kepler has returned to Earth.

We’re pretty sure there are billions—billions—of Earth-sized planets in the galaxy. We now know of four that are in their star’s habitable zone (if you include Venus and the other planet I mentioned)… and we also know that some worlds are outside the strict definition of the HZ and yet still have liquid water (Jupiter’s moon Europa and Saturn’s moon Enceladus).

We’ve only just started looking. Who knows what else is out there?

Tip o’ the Lyot stop to Stephen Kane (one of the astronomers who found this planet, for his gracious help with info; go check out his website, Habitable Zone Gallery) and to the lead author Elisa Quintana.

Everything You Need to Know to See Monday Night's Lunar Eclipse

Slate

Bad Astronomy

The entire universe in blog form

April 12 2014 7:30 AM

Don’t Miss the Lunar Eclipse on April 14/15!

By Phil Plait

One of my all-time favorite lunar eclipse pictures. Click to umbranate.

Photo by Laurnet Laveder, used by permission

Do you live in North America, South America, Australia, or eastern Asia? Then you get to see a lunar eclipse on the night of April 14/15! And while North America is the best place to watch—we’ll get to see the whole event—the real action doesn’t begin until 05:58 UTC on the 15^th, which is just before 02:00 EDT, so it’s a bit late. You might just want to stay up for it, though.

 

 

A lunar eclipse is when the Moon slips into the shadow of the Earth and gets dark. Unlike a solar eclipse (where the Moon blocks the Sun) a lunar eclipse lasts for hours and is perfectly safe to observe without protection. In fact, I find using binoculars is best!

How does this work? The Sun lights up the Earth (big duh there), and anything that’s illuminated casts a shadow. Normally the Earth’s shadow just goes off into space, but sometimes the geometry works out that the Moon passes into it. The Moon has to be opposite the Sun in the sky for that to happen, so lunar eclipses only happen when the Moon is full.

Schematic showing the geometry of a lunar eclipse. not to scale (duh).

Drawing by Shutterstock / fluidworkshop

The Earth actually casts two shadows; a wide, fuzzy one called the penumbra, and a narrower, darker one called the umbra nested inside the penumbra. If the Sun were a point source in the sky (a little dot) there would only be one dark shadow, but because the Sun has a finite extent (that is, we see it as a disk) the geometry is a little more complicated. If you could see the shadows in the sky, the penumbra would be a big circle about five times wider than the Moon, and the penumbra would be a circle inside it about half that size.

By taking several exposures during a partial lunar eclipse in 2008, Anthony Ayiomamitis was able to create a mosiac showing the Earth's umbra cast into the sky.

Photo by Anthony Ayiomamitis, used by permission

It helps to think of it from the Moon’s viewpoint. If you were standing there, looking back at the Earth and Sun, you’d see the Earth (barely; you’re seeing it’s night side) sliding slowly over the face of the Sun. At the moment the edge of the dark Earth starts to block the sun, you’re entering the penumbra. It’s getting darker, but most of the Sun is still unblocked, so it’s not getting very much darker.  About an hour later the Earth completely blocks the Sun, and you’ve entered the umbra. The Earth is much bigger than the Sun from your point of view (about four times larger) so the Sun stays blocked for a while. Finally, the Sun peeks out the other side of the Earth; you’ve left the umbra and are in the penumbra again, and things start getting brighter.

A lunar eclipse... seen from the Moon! This was taken by the Japanese Moon probe Kayuga in 2009, and shows the Earth eclipsing the Sun.

Photo by JAXA/NHK

What does this mean for us here on Earth? We’ll see the Moon enter the penumbra at 04:53 UTC April 15, or 00:53 EDT (53 minutes after midnight). Again, it’s no big deal, and you’d hardly notice. But the Moon’s edge enters the darker umbra at 05:58 UTC (01:58 EDT) and over the course of a few minutes you’ll see that part of the Moon get dark. Over the next hour or so more of the Moon will fall into the Earth’s darker shadow, and at 07:06 UTC (03:06 EDT) the entire Moon will be dark. It’ll stay that way for the next hour and 18 minutes, until it starts to move out of the umbra at 08:24 UTC (04:24 EDT), and will start to be illuminated by the Sun again. The umbral eclipse ends at 09:33 UTC (05:33 EDT).

Here’s a diagram that may help:

How the eclipse will play out; the description is in the text below. Click to embiggen.

Diagram by Fred Espenak / NASA (modified for clarity by Phil Plait)

The Moon moves from right to left in the diagram. The positions are labeled. P1 is when it moves into the penumbra, U1 is when it moves into the umbra, U2 is when it’s fully immersed, U3 is when it starts to leave the umbra, U4 is when it’s out of the umbra, and P4 when the Moon leaves the penumbra, and the eclipse ends. The times are listed in the lower right in UTC. Subtract four hours for Eastern US time, and so on.

Sometimes when the Moon is fully immersed in the Earth’s shadow it can turn an eerie blood red due to the way the Earth’s atmosphere scatters light — it’s the same reason the Sun can look redder at sunrise and sunset.

Want to hear something poetic? If you were standing on the Moon during the deepest times of the eclipse, from your view you’re seeing all the sunrises and sunsets on earth at that moment.

When someone tells you science is cold and emotionless, tell them that.

The only problem with this eclipse is the timing; it happens late Monday night/early Tuesday morning for most of the US. But don’t let that stop you! If you have clear skies you really should go out and look. And if you have a camera, please take some pictures! With a little planning you can get some amazing shots like the ones I’ve scattered through this post (see Related Posts below for many more). Check out this incredible time-lapse animation made by Jeffrey Sullivan of a lunar eclipse in 2011:

Observing the Moon with a telescope or binoculars during an eclipse is a wonderful thing, but if you only have your eyes, that’s fine too. It’s fun to go out every few minutes between U1 and U2 and watch the Moon get eaten by the Earth’s arcing shadow.

I hope you have clear skies and good viewing for this event! And if you don’t, never fear: There’s another one in October, then a third in April 2015, and a fourth in September 2015 too. You’ll have plenty of chances to see this lovely astronomical bit of geometrical alignment over the next year and a half.

Related Posts

Incredible Lunar Eclipse Floats Near the Lagoon (phenomenal photo!)
Lunar Eclipse Time-Lapse
Discovery Eclipse
STUNNING Lunar Eclipse Photo
A Lighter Shade of Umbra

The Red Planet Hasn’t Looked This Good in Years

Slate

Bad Astronomy

The entire universe in blog form

April 10 2014 7:45 AM

Mars at Its Best Right Now

By Phil Plait

Mars glows like a red demon's eye in the sky right now.

Photo by Christian Fröschlin, from the video

Due to the orbital dance of the planets, Mars is currently at its best showing of the year, as close to Earth as it gets, and shining brightly all night long.

Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death from the Skies!

To see it, go outside. If it’s after sunset and the sky is dark, face southeast. Look up. There it is. It’s one of the brightest objects in the sky and shines with an orange-y glow.

The technical term for Mars’ place in the sky right now is opposition because it is opposite (literally, 180° around the sky) from the Sun. The Sun sets in the west, so after sunset look east. At midnight, when the Sun is lowest, Mars is at its highest. And closer to dawn as the Sun begins to rise in the east Mars will be sinking in the west.

The orbits of the inner planets as of April 9, 2014. Earth (blue) and Mars (red) are indicated, and they form a straight line with the Sun.

Diagram by Heavens-Above

This also means the Red Planet is as close to our own blue-green one as it gets for a couple of years, so it’s the best time to observe it. Mars is only half the size of the Earth, and more than 90 million kilometers (45 million miles) away, so it’s still rather small through a telescope. Despite that, astrophotographer Christian Fröschlin used his Celestron 8” telescope to observe Mars on April 9, 2014, creating enough images to string together into this amazing video:

Coooool. You can actually see the planet rotate! Mars spins once on its axis in a very Earth-like time of about 24.5 hours (what planetary scientists call a sol to distinguish it from an Earth day), so you’re seeing roughly 1/8^th of a sol here. It’s currently summer in the Martian northern hemisphere, so that half of the planet is tipped toward the Sun; that means you’re seeing the north polar ice cap in the video. You can see a bunch more recent images taken of Mars over at Universe Today.

Mars isn’t far from the somewhat fainter orange giant star Arcturus in the sky, and it’s fun to compare them. Also, on Sunday and Monday the full Moon will be only a few degrees away, so that’ll make a good photo op.

If you have clear skies, get outside and look up! The Universe awaits.

April 8 2014 12:30 PM

No, That’s NOT an Artificial Light on Mars

By Phil Plait

Apparently April is the month to debunk astronomical foolishness, for I have yet another bit of space silliness to disassemble.

Yesterday, the Houston Chronicle ran a story showing a picture from the Mars Curiosity rover, which has been exploring the fourth rock from the Sun since August 2012. As the rover moves over the Martian surface it deploys an arsenal of tools to examine its environment.

That, of course, includes cameras. Many of the pictures are visually stunning, and some are plain old weird. After all, they’re shots of the landscape on an alien world!

But some folks take the word “alien” a bit too metaphorically. In the Chronicle article, the writer, Carol Christian, points out one particular picture (shown above) that depicts a spray of light that looks to be off in the distance. She wrote, “A NASA camera on Mars has captured what appears to be artificial light emanating outward from the planet's surface.”

Right, artificial. That’s the first conclusion we should jump to. But then, instead of asking any of a dozen scientists or science journalists who might actually be able to supply an answer, she just quotes the site she got the image from: UFO Sightings Daily.*

Yes, you read that right. The Houston Chronicle is repeating a story they found on a UFO conspiracy site.

When I saw the picture, I knew right away it wasn’t from some artificial source. It wasn’t even really a light source on Mars! I’ve worked with astronomical cameras for many, many years, and we see little blips like this all the time. To make sure though, I asked my friend Emily Lakdawalla, who is also a planetary scientist and journalist. Her immediate response: cosmic ray.

[UPDATE (Apr. 8 at 20:00 UTC): The plot thickens; Justin Maki, a scientist at JPL, says this may be a sunglint off a rock, and not a cosmic ray. That's certainly possible! As I note below, though, it only appears in one camera and not the other, so I'm not quite convinced yet. However, I'll wait a little while and see what shakes out of this, so I don't post a lot of confusing updates and corrections! In the meantime, even if it isn't a cosmic ray I can still be reasonably sure it's not aliens.]
 

Ah, of course. Cosmic rays are charged subatomic particles (like protons, electrons, and so on) zipping around in space. On Earth, our atmosphere absorbs them so they don’t have much of an effect on cameras down here. But if you put a telescope in space, they are bombarded by these little beasties. When a cosmic ray slams into the electronic detector in the camera, it deposits some energy in the pixel (or pixels) where it hits. These detectors are designed to detect energy from incoming light, and they can’t tell the difference between a cosmic ray hit and a photon coming from a distant star. All they do is register the energy (you can read a lot more about this on a page where I dismantled claims about Planet X).

And that’s what we have here. Curiosity was taking a picture of the Martian horizon, and during the time the picture was taken, a subatomic particle smacked into the camera, leaving behind its trail of energy. It’s a camera artifact, not a real one.

Photo by NASA/JPL-Caltech

How can I know the light isn’t real, and is just inside the camera itself? Because the camera is the NAVCAM, which is actually two cameras, one on the right and one on the left. This provides a binocular view of the landscape, which can be used (just like our own eyes do) to determine distances to objects. At the same time NAVCAM RIGHT took the picture with the light in it, NAVCAM LEFT also took a picture … and there’s no light. Here are both pictures so you can compare them:

See? It’s in one camera’s picture but not the other, even though they were taken at the same time (on April 3, 2014, at 10:00:03 UTC).

To make this even more clear, I made an animated GIF of the two shots:

As you can see, the landscape shifts a bit due to the different perspectives of the two cameras. The light is in one shot, but not the other.

I’ll note we see this kind of thing all the time, including in Curiosity images. Here’s one over a rock, for example. It’s not hard to find more if you peruse the Curiosity raw images archive (or the Unmanned Spaceflight forum, where space aficionados post and discuss the latest images from various missions).

So that’s what we have here. It’s not some alien rave, or a stranded bug-eyed monster signaling for help, or other fanciful fiction. No, it’s far more mundane, merely the quantized energy deposited by a subatomic particle that was accelerated in the magnetic fields of an exploded star and traveled thousands of light years across the galaxy at nearly the speed of light to finally slam into an electronic camera mounted on a mobile nuclear-powered laser-eyed chemical laboratory humans sent to another planet.

Clearly, reality’s not cool enough. We need to add aliens to make this a story.

Sigh.

(My very sincere and very large thanks to Emily Lakdawalla for help on this.)

April 7 2014 11:00 AM

Follow-Up: The Meteorite and the Skydiver

By Phil Plait

Last week, a video went viral that purports to show a skydiver narrowly missed by a meteoroid falling past him. A lot of people have been speculating over the video, of course. I watched it many times, and after giving it some thought I wrote up my own opinion. Basically, the video doesn’t looked faked to me, and while I remained skeptical, I leaned toward it being real, and open to the idea that it really is a meteoroid.

Note: If this rock came from space then technically it was a meteoroid; they’re called meteorites after they hit the ground. I took great pains in my first article to call it a rock or an object, since its pedigree is still up in the air. I will do so again here. However, most of the articles I saw called it a meteorite, so I used that term in the titles so people would know what video I’m talking about.

Here's the footage again; you can see the object fly past at about the 1:50 mark.

Over the weekend I received lots of comments on Twitter, Facebook, and via email about the video and my post. Some of them were from people convinced the object is a meteoroid, while others poo-pooed the whole idea. But some of the discussion went into details of the video and what it could be, and I want to follow-up on what I wrote because of that.

To be clear and concise: While I initially dismissed this idea after some thought, it is entirely possible that what the video shows is a smaller rock that fell out of the skydiver’s parachute. I don’t think this can be ruled out, and indeed, is more parsimonious than the idea that the video captures an extraordinarily rare event like the dark flight of a meteoroid. So the video is almost certainly real, in that I mean it wasn’t hoaxed, but as things stand now we cannot know for sure what the object is or isn’t. But it being a rock trapped in the ‘chute is a far more likely explanation.

Well, ‘Chute

In my first post, I brought up the idea that the object was a bit of debris caught in the parachute, and then fell out when the parachute opened. However, given the size and speed of the object, that seemed unlikely to me, so I discounted it.

I may have been too speedy in that assessment. First, many skydivers have said falling debris is a relatively common event; all manners of small objects can get caught in the parachute when it is packed on the ground before the dive. So it’s not impossible, and there’s plenty of precedent.

Second, I discounted the idea of this being such an object due to its size. An analysis of the video by Steinar Midtskogen indicated the rock was between 8-20 cm (3-8 inches) across. Surely something that size (and weighing 1-20 kilos) would not get missed when the ‘chute was being packed!

But Midtskogen was assuming the object was a meteoroid, and falling several hundred kilometers per hour, terminal velocity for such an object. The speed it falls is critical for getting its distance from the camera (the object moves rapidly across the camera field of view, so if you know how fast it is moving then you can calculate how far it falls between video frames, and that can be used to determine its distance from the camera). He finds it was between 2.5 and 6.5 meters (8-21 feet) away when it passed.

But that assumes the object really is moving rapidly. If it fell from his ‘chute, then it could easily be moving much less quickly, and that would mean it was actually much closer to the camera, and therefore smaller. I didn’t initially think this would be the case because the object is well-focused in the video, and if it were really close it wouldn’t be.

That was an error on my part. The camera used is wide-angle and has a very large depth-of-field, the technical term used to mean the range of distance over which an object is focused. As you can see in the frame grabs from the video, the hand straps and tethers in the parachute are well-focused, and are less than a meter away from the camera! That means the object too could have been less than a meter away, which means it could have been much smaller, as small as just a couple of centimeters.

My friend and astrophotographer André van der Hoeven also analyzed the video, and determined the object was not accelerating when it flew past; in other words it was at terminal velocity. He reasoned that a rock falling from the parachute would be expected to accelerate due to gravity, so he concluded it must have fallen from far, far above the diver. [Update (Apr. 7, 2014 at 16:00 UTC): van der Hoeven recently updated his analysis to note that he can't rule out the rock coming from the parachute, only that it was unlikely.]

However, there are a lot of variables to this. At the speed at which the skydiver was falling, air resistance would be quite high and could slow a small rock very rapidly. There could also be quite a bit of turbulence from the parachute itself, creating eddies in the air that could change the velocity of a small falling rock. I don’t think we can rule out the possibility of it being debris initially stuck in the ‘chute due to the speed and/or acceleration at which it falls.

And I have to admit that it bugged me right away that we see the object just seconds after the parachute deployed. That’s another big coincidence in a big series of them. At first the evidence seemed to weigh against it coming from the parachute, but now it’s clear that’s not the case.

The hot, glowing phase of a meteor's fall only lasts for a few seconds and occurs high in the atmosphere; after that the rock cools and falls at terminal velocity, a few hundred kph.

Photo by Mark Gee, used by permission

[Update 2 (Apr. 7, 2014 at 17:30 UTC): Dr. Philip Metzger a physicist and planetary scientist at NASA, analyzed the video using some sophisticated computer modeling and determined that the object was most likely either a small piece of rock very close to the camera, or a far larger one between 12-18 meters away. Given how big the object must have been if it were really that far away, this again lends more weight to the idea that this was actually a small bit of debris caught up in the parachute.]

Earth Diving

In my first article, I was more concerned over whether this was a hoax than a case of mistaken identity. That gave me a certain angle, a certain point of view, while looking over the video. I should have been more concerned over the possibility that while the video was authentic, the conclusion was mistaken.

After more thought, I not only cannot rule out that it was a smaller rock caught in the parachute that fell once the ‘chute deployed, I have to admit that it is a more likely explanation. That does not mean it’s the right one, of course. But bear in mind that meteoroids big enough to see are extremely rare, and are so uncommon that none—not one—has ever been positively caught on video, despite all the cameras we use all the time. That means this object is even more unlikely to be one, since it also fell very close to the camera (and coincidentally right after the parachute opened). That’s a whole lot of unlikely events happening in a row, which triggered my skeptical sense right away but makes it tingle even more strongly now.

I’ll note that Midtskogen emailed me over the weekend and was quite open about this possibility, and is eager to have others analyze the video to see what they can find; they put all the original footage on YouTube (though the original raw footage off the camera is not available yet; it’s too big for YouTube, but Midtskogen assured me they’re working on a home for it). That is precisely the right attitude, and I hope that other people can find clever ways to figure out more about this.

And finally, another observation: As usual, with a claim on the Internet, the reactions to it have been diverse, fascinating, and frustrating. From the comments I received, I found a lot of people didn’t really read what I wrote. Some people thought I was saying it is definitely a meteorite—but that’s not the case. I tried very hard not to say that in my post (though my concluding paragraphs are based on the idea that it was). Others were dismissive of the idea, saying that a meteoroid would still be hot and moving at hypersonic speeds, a misconception I specifically debunked in my article!

It was nice to see much of the commentary being calm and rational, with different people picking up various threads and analyzing them for their merit or lack thereof. Of course that wasn’t always the case, and some folks got pretty hot under the collar about this. But that is less than useless; it turns people off and can close avenues of discussion that might otherwise be useful. In a case like this, simple, reasoned discussion is the best way to go.

I’m still willing to be swayed further either way on the topic. I am not saying it was or was not a meteoroid, but it seems far more likely to have a far more mundane explanation. And either way, any conclusion will have to rely on better evidence and better, more detailed analysis than we have seen so far.

But if I had to bet, based on what we’ve seen? I’d put my money on it being a plain ol’ rock.

The entire universe in blog form

April 3 2014 7:45 AM

Fly Into Hubble’s Universe!

By Phil Plait
 

The talented astronomical artists at the Space Telescope Science Institute have been pouring the gorgeousness of Hubble pictures into our eyes and brains for years. They recently embarked on a new venture: Taking those same images and, using complementary data to get more information about the objects, creating stunning 3-D animations. Mind you, these are not “real,” but visualizations based on actual data that approximate the view you’d have if you could fly around the Universe at multiple times the speed of light.

Here’s one they made of one of my all-time favorite celestial sites, Sharpless 2-106, the birthplace of a massive star:

Note: I added the notes and the music.

I’ve written about SH 2-106 a few times (see Related Posts below), because it’s a fascinating object as well as one of the most beautiful images Hubble has produced. While this animation isn’t exactly real, it does give you a sense that you’re seeing a huge star that’s carved out tremendous cavities in the surrounding gas. That’s difficult to see in the usual two-dimensional static images, so while these visualizations are in some ways flights of fancy, I think they provide a useful tool to better understand astronomical objects.

There are several more videos like this at hubblesite.org, so I urge you to go take a look. They’re quite lovely.

Related Posts

Epic Tantrum Thrown by a 30 Octillion Ton Baby
The Brush Strokes of Star Birth
When a Star Struggles to Be free of Its Chrysalis

The entire universe in blog form

April 2 2014 11:30 AM

Flash of Illumination

By Phil Plait

From space, the Earth is seen from above, literally taking on a new perspective that can make our home planet itself look like an alien world.

In 2011, an astronaut onboard the International Space Station took a photo that proves it.

A Bolivian thunderstorm seen from above and far to the side. Click to encumulonimbusate.

Photo by NASA

That is a thunderstorm over Bolivia, seen at an oblique angle. It was nighttime there, and normally you’d only see the soft orange glow of city lights. However, at the moment the astronaut snapped the photo a lightning bolt tore through the cloud, illuminating it from within. It also lit up surrounding clouds as well as what looks like some water to the side (though it’s hard to be sure).

I remember when that picture was taken and being impressed with it, but for some reason I never put it up on the blog. I’ve fixed that oversight now. I love shots from space of Earth’s weather, from clouds casting long shadows to hurricanes casting a pall over entire countries. The images are beautiful, powerful, and a reminder that sometimes to see something so close and large, you need to back up a bit and take it all in from a different angle.

Tip o’ the space umbrella to NASA Earth Observatory on Twitter.

Explore a 680 Gigapixel Map of the Moon’s North Pole

By Phil Plait

If you zoom in enough, you can see Santa's summer home. Click to enselenate.

Photo by NASA/GSFC/Arizona State University

The folks on the Lunar Reconnaissance Orbiter Camera team just released an unbelievable image of the Moon: A 680 gigapixel mosaic showing details of the lunar north pole down to two meters across!

The mosaic is available as a scan-and-pan interactive page, where you can zoom in and sweep across the moonscape. There are a few interesting spots listed that you can click and zoom right to, like this lovely (and, judging from the fresh rays and sharp contours, relatively young) crater:

They're so cute when they're young.

Photo by NASA/GSFC/Arizona State University

You can zoom in pretty far, and I suggest making it full screen. It’s almost overwhelming at that size.

The mosaic is a combination of 841 tiles; the raw file (which, understandably, they don't make available for download) is well over three terabytes in size. As for the original images, LRO is in a polar orbit around the Moon, meaning it’s moving in a mostly north-south manner. As it orbits, the Moon slowly spins underneath it, so eventually LRO sees the entire lunar surface. Due to the geometry of the orbit, this means the terrain it sees at a given latitude has roughly the same lighting. That’s important: A crater looks very different when the Sun is low (and shadows long) compared with at noon, when the Sun is high (and shadows nonexistent).

So you can think of the mosaic as made up of a series of concentric rings of parallel longitudes, each with about the same Sun elevation, with the Sun getting lower as you move northward (because at any given time, the Sun is lower the farther north you go). That’s why the overall mosaic looks flatter near the edge and bumpier in the middle: At the pole the shadows are longest, and you see the contours of the terrain better.

And how much of the Moon does this mosaic cover? A total of 2.5 million square kilometers, or just about a million square miles! That’s a lot of Moon. To give you an idea of the area, here’s the mosaic overlaid on a map of the United States:

If you get caught between the Moon and New York City... Click to enarthurnate.

Photo by NASA/GSFC/Arizona State University

Yegads. And all of that is mapped, down to a resolution of a few meters per pixel. That’s astonishing. And it makes me wonder: Will future explorers use maps like this as they bounce around the Moon’s surface, prospecting, or running experiments, or simply going out for a stroll?

March 12 2014 7:30 AM

The Glory of Venus

By Phil Plait
 

It’s not too often that I get to combine two of my true loves … like astronomy and weird optical effects.

My love of astronomy should be pretty obvious, and if you’ve read this blog (or follow me on Twitter and Facebook) for more than about eight nanoseconds you know I love me some optical illusions, iridescent clouds, light pillars, halos, parhelia, and more.

So I’m actually pretty happy to be able to show you a mashup of the two that is not only pretty cool, but also scientifically useful: a glory on Venus.

Behold! Weird splotchy color thingies on another planet!

Photo by ESA/MPS/DLR/IDA

That decidedly weird picture is from the European Space Agency’s Venus Express, a probe that has been orbiting our hellish sister world since 2006. On July 24, 2011, the spacecraft took this image while looking straight down into the planet’s thick atmosphere when the Sun was directly above it. Why is that important?

A glory is an optical phenomenon, where light is bent by tiny droplets in the air. This is similar to how a rainbow works, but in this case the exact mechanism is still under debate. For the effect to work the Sun has to be directly behind the observer and shining into a bank of liquid droplets. The light gets broken up into its individual colors, which form concentric circular halos centered on the shadow of the observer’s head (or more technically the anti-solar point). They’re pretty commonly seen from airplanes; I’ve observed them many times when the Sun is shining down on the opposite side of the plane, and I can see clouds and the plane’s shadow out my window.

The size of the halo and the colors depend on the size of the droplets and the amount they bend light, which depends on the chemical composition of the droplets. On Earth, of course, we’re talking water, but on Venus it’s not so easy. The majority of the atmosphere there is carbon dioxide, but there are a myriad of other molecules floating around there as well, making it rather difficult to determine what’s what in the thick murk.

This image of the glory may help figure that out; we know the optical properties of the gases in the atmosphere of Venus, so a computer model can be made to simulate those conditions (pressure, temperature, composition, and so on) to hopefully narrow down the possible sources of this optical effect. At the moment that work is ongoing.

Not a glory, but still cool. Click to encronosenate.

Photo by NASA/JPL/Space Science Institute

To my knowledge this is the first time a glory has been seen on another planet; a similar but different effect in Saturn’s rings nearly fooled me once a while back, and it’s even been seen on Earth from space! But a true glory on another planet hasn’t been detected until now.

Pretty cool. This never would have occurred to me to look for in the data, which shows me that we have very, very clever people out there who are trying to squeeze every last gram of useful information out of our probes in space. That’s just as it should be! You never know what treasures are hidden there.