5 things to know about ESA’s Rosetta Mission

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Sep 30, 2016, 4:49 PM EDT

In March of 2004, the European Space Agency (ESA) launched the Rosetta spacecraft on a journey to orbit and study the Comet 67P/Churyumov–Gerasimenko. It reached its target a decade later, executing its last command early this morning. All of space Twitter collectively teared up as we said our final farewells to this incredible mission. Before its final dive into the comet, Rosetta gifted the science community with a few more final images of space porn that will undoubtedly be examined and dissected for years to come.

If any of this is news to you or you’re keen to know more about Rosetta, here are five things you should know.


1.SPOILER: It’s over.

This morning at approximately 7:19 a.m. EDT, the Rosetta spacecraft “touched down” on the surface of Comet 67P/Churyumov–Gerasimenko, effectively ending its 12-year mission. The final hours of the spacecraft were spent photographing features on the comet with unprecedented detail as it got closer and closer. Prior to its swan song, the lowest closest orbit had only taken Rosetta within ~30km of the comet’s surface.


2.Why we sent a spacecraft to a comet

The Rosetta mission was conceived by the European Space Agency (ESA) to perform the most detailed study of a comet to date. Comets are interesting because they are believed to be the “leftovers” from the formation of our solar system.  They are essentially smaller bodies that never got accreted by the bigger bodies that became the planets we know today.

Comets likely formed on the outskirts of the solar neighborhood, so their lives have been cold and dark. Therefore it’s a good bet they’ve hardly changed at all over the past 4.5 billion years; they are like perfectly preserved time capsules that can tell us the ingredients in the original solar nebula we were born from. We know the majority was hydrogen and helium (or the sun wouldn’t exist), but we’re more interested in the materials important for life: water, carbon, iron, as well as volatiles (frozen compounds that can be released when heated).  Knowing how much of each element or compound there was to start can tell us more about how those elements and compounds combined in various ways to result in the solar system we see around us.

Believe it or not, how planets form is still a big open question in astronomy. There are a lot of theories and we have a general picture, but the details of where and when gas giants form versus terrestrial planets are a lot harder to nail down. If we can better understand how Earth-size and Earth-like planets form, we can better search for them around other stars.


3.Did Rosetta go to the outer reaches of the solar system?

It didn’t have to. While many comets spend most of their lives in a spherical reservoir we call the Oort Cloud, a fraction of them have their orbits perturbed and are sent on trajectories into the inner solar system. Another fraction of comets live considerably closer in, in a region called the Kuiper Belt, which I like to refer to as a larger, icier, more distant version of the asteroid belt. Comet 67P is believed to have originated in the Kuiper Belt, but thanks to a few close encounters with Jupiter sometime in its past, its orbit has been altered. The comet’s current elliptical orbit takes it inside the orbit of Mars on closest approach to the sun and just outside Jupiter’s orbit on the other extreme.

Discovered less than 60 years ago by Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko in 1969, Comet 67P orbits the sun every 6.45 years and is only about 2.5 miles by 2.7 miles at its widest points (that’s bigger than Central Park, but only a quarter of the size of Manhattan). Rosetta rendezvoused with the comet in the fall of 2014 when it was roughly 3 AU (astronomical units) from the sun (just under 300 million miles) and traveling towards the sun. It then spent the next 22 months orbiting Comet 67P and doing all the science. When it touched down on the comet this morning, both objects were around 3.5 AU from the sun, but now heading in the opposite direction.


4.Back to that landing part again … that actually happened.

Twice! The first landing was in November of 2014, when Rosetta’s traveling companion, the Philae lander, was released from the main spacecraft and touched down on Comet 67P.  Philae was like Rosetta’s sidekick, it went along for the ride when the mission launched in 2004 and when they arrived at the comet, there was a division of labor: Philae went down to take a closer look while Rosetta stayed in orbit to keep an eye on things.

Philae was designed to do four-five months of science from the surface of the comet, but unfortunately the harpoons that were supposed to anchor it upon touchdown didn’t fire and because of the extremely low surface gravity of the comet, it bounced twice before coming to rest over half a mile away from where it first hit. Unfortunately the angle the ended up in didn’t allow its solar panels to charge effectively, so all communication was lost with a couple days when its on-board batteries died. The ESA team had a rough idea about where Philae was but it wasn’t until earlier this month that Rosetta’s camera was able to spot its actual location among the comet’s nooks and crannies.

As of this morning, Rosetta is now reunited with Philae (within x miles at least) on Comet 67P. Rosetta wasn’t designed to land on the surface like Philae, but its touchdown was as controlled a possible and I like to think it went somewhat better than this.


5.How can you find out MOAR?

ESA’s PR machine killed it for this mission. They created a wonderful animated video series depicting the adventures of Rosetta and Philae. You can find them all here. I highly recommend watching them in order. And after you watch the last one, there’s a good chance it will be raining on your face.

The view from Rosetta’s final descent can be found here. But really all the stunning images of Comet 67P taken by Rosetta as it rounded the Sun are also worth a look.



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