Long Way Home

By Phil Plait Feb. 10 2014 7:45 AM

Earth, from Mars — A spark of light, barely seen, yet it means the world.

There is something about home that calls out to us, so much so that no matter how far out we may travel, there is an irresistible urge to turn our heads and gaze back from whence we came.

We do it when we climb mountains, when we leave shore to explore the ocean, and when we send our robot proxies into space, out into the black, never to return.

Such was the case for Curiosity, our nuclear powered mobile chem lab making its way across the surface of Mars. Certainly, scientists have been avidly studying the remarkable close-ups of the ground beneath Curiosity’s wheels, the terrain it must cover, and the distant peak of Mt. Sharp looming many kilometers away.

But that urge to look home could not be dissuaded. On Jan. 31, 2014, the camera perched atop Curiosity’s tall mast was turned to the sky, toward sunset, where two bright stars appeared … but these weren’t stars.

That image shows the hilly Martian horizon silhouetted against the darkening sky. And in that sky are two points of light: the Earth and Moon. They’re hardly visible here; but they shine better in the full resolution image.

From a distance of nearly 160 million kilometers (100 million miles), these two worlds are reduced to mere points. From the point of view of Mars, Earth was an evening star, setting after the Sun. Also from Mars’ vantage point the Moon was separated from the Earth by about as much as it could be (the Moon was new to us), so it’s cleanly seen apart from the stellar dot of its mother planet.

It’s hard to imagine our entire world reduced to a dot. When we go outside, we’re standing on it, and it fills half the sky. Perhaps you’ve never thought of it that way, but it’s true: Were the Earth not there, you’d be surrounded by sky, even under your feet. Our planet, huge and opaque, blocks half our view of the heavens.

But go far enough away, and even a world nearly 13,000 kilometers across dwindles to a spark of light in the sky. And bear in mind, Mars is one of the closest astronomical objects in the solar system, let alone in the cosmos. On a galactic scale, even our mighty Sun fades to invisibility before you venture very far out into the Milky Way. And our galaxy—among the largest in the Universe—would take a huge telescope to see at all from the most distant objects we see.

The Universe is terribly vast, hugely distant, cold, and indifferent to us.

But remember this: The picture above was taken by a machine made by humans, and it’s sitting on the surface of another world. It took hundreds of people thousands of worker-years to imagine it, lobby for it, create it, loft it, and land it on Mars. You can’t see that in the picture because the camera was turned the other way. But if you can step out of the picture in your mind and simply turn around, you’d see that rover on the Martian dust, a testament to human curiosity, the drive to explore, and the need to leave the nest for parts unknown.

It doesn’t bother me in the least that the Universe doesn’t know or care about me. I know and care about it. And that’s what counts.

Labels: Astronomy, Nature, Science, Universe