Farewell to Rosetta

Today, the Rosetta space probe, which had been in orbit around Comet 67P/Churyumov-Gerasimenko for just over two years, was deliberately steered into Comet 67P for a crash landing, ending the mission.

Credit: ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0

Now, when I say crash landing, that's a bit of an exaggeration. Comet 67P doesn't have a lot of gravity, so instead of some big, spectacular crash, with debris flying everywhere, the collision looked a little more like this. And much like the Philae lander, Rosetta probably did its fair share of bouncing before it finally came to rest.

So, what's the reasoning behind ending the Rosetta mission? It's simple, really, Rosetta is solar powered, and Comet 67P is moving away from the sun. The solar panels simply aren't big enough to sustain Rosetta out past the orbit of Jupiter. I'm not exactly sure why Rosetta has to be crashed into the comet, but what do I know?

So, Rosetta then! It was an ambitious idea, getting a space probe in orbit around a comet. After all, comets are very small and have big, highly elliptical orbits. We've visited comets in the past, starting in 1986 when Giotto and Vega 1 and 2 flew by Halley's Comet. But Rosetta was different. And it took its sweet time doing it, too. Rosetta was launched in 2004, but didn't establish orbit until 2014. Now, Rosetta has made plenty of useful observations, and the scientists still have a lot of data to go over, but that's not why people know about Rosetta. No, people know Rosetta because of Philae, the little lander that Rosetta dropped on the comet.

Now, to be honest, Philae wasn't very successful. The probe was supposed to attach itself to the surface via harpoon, but the harpoons failed, and the probe bounced from its designated landing spot to a much less hospitable spot underneath a cliff in basically permanent shadow. This was not the best spot for a solar powered probe, and after a couple of days, the onboard batteries were dead. Philae made intermittent contact whenever it came back into the light in June 2015, but nothing firm was established, and final contact occurred not long afterward. From a scientific standpoint, Philae was a disappointment. Most, but not all of the science got done, but considering the runaway success of some of the other space probes out there, three days of operation when weeks or months were expected is a letdown. But that's not what people will remember. No, people will remember the plucky little space probe that travelled millions of miles to go land on a comet. In our social media age, its Twitter might have helped.

So, here's to Rosetta and Philae. The space probes that voyaged across the inner solar system for 10 years to meet a tiny little comet, and tell us all about the history of our solar system.

How Recently Did Mars Have Liquid Water?

Science is very hard. You think you know something, you think you've got things all figured out, but then you get some more information, and that previous assumption just goes flying out the window. Case in point: last year, I wrote about how the MAVEN space probe had studied the Martian atmosphere and determined that the pleasant Mars with a substantial atmosphere and abundant liquid water was gone nearly 4 billion years ago, and for most of Mars' history, it's looked pretty much the same as it does now. It was simple, it was elegant, and while it wasn't really good news, it fit the data we had.

You can probably see where this is going. As it turns out, there are valleys and basins on the Martian surface that were formed by liquid water, but formed a billion years after the Martian atmosphere was lost to space, and the planet's surface became too cold to host liquid water. We're not talking about an insignificant amount of water either, there was enough water in one of these lakes to fill Lake Erie and Ontario with water to spare. The valleys running into these basins are not as complex as the older river valleys, indicating a slower flow. This probably indicates the lakes were filled not with rain, but with runoff from fallen snow.

This is obviously a bit of great news. If water could stay liquid on the Martian surface 2 billion years ago, that means that it was potentially habitable for the same amount of time. That is a much longer timeframe then we previously thought. 500 million years is not a huge amount of time for life to evolve, but 2 billion years is a lot more generous. Of course, it also raises into question the findings of MAVEN. Was the atmosphere gone by that point? Where did all the snow come from? Mars just got a lot more interesting.