Category Archives: comet

comet, Comet 67P/Churyumov-Gerasimenko, rosetta, rosetta spacecraft

The Rosetta Mission at Comet 67P Will Soon End

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Studying a Comet Long Term

This four-image montage shows the spectacular region of activity at the 'neck' of 67P/C-G. This is the product of ices sublimating and gases escaping from inside the comet, carrying streams of dust out into space. ESA/Rosetta/NAVCAM
This four-image montage shows the spectacular region of activity at the ‘neck’ of 67P/C-G. This is the product of ices sublimating and gases escaping from inside the comet, carrying streams of dust out into space. ESA/Rosetta/NAVCAM

I’ve been a comet fan since my grad school days. That was when I got pointed at Comet Halley and told, “study these images, and let’s figure out what’s happening with the plasma tail”. So, I pored over images of the comet taken from 1985-1986. I made lots of measurements and worked on papers with my team members. Eventually, we figured out what was happening with the plasma tail (hint: it’s affected by the solar wind). It was a pretty exciting time in my life, standing at the “frontier” of comet science (at that time) and opening my mind to the idea that what happens in the solar wind can make intricate “designs” in the shape and behavior of a plasma tail.

During that whole time, I was also intrigued by what a comet REALLY looks like. We didn’t have any close-up pictures of a comet nucleus. Sure, we had the Fred Whipple model of a chunky block of dusty ice (or icy dust, if you prefer) to study. And, there WERE some Giotto spacecraft images of the Halley nucleus. But they had to suffice until we could get REAL close-ups. What was needed was a long-term study of a nucleus. That’s what the Rosetta mission has done at the nucleus of Comet 67P/Churyumov-Gerasimenko.

Rosetta Orbits a Piece of Solar System History

For the better part of two years, the Rosetta spacecraft has visited the comet. It studied the chemical composition, sent back images, and gave astronomers the longest “timelapse” look at a comet ever. Along with its Philae lander, which functioned for only a short time, Rosetta is a great achievement. It’s something the European Space Agency and scientists around the world can be very proud to have sent. They’ve orbited a major piece of solar system history. They opened a window into the distant past when comets formed from materials that existed before the Sun and planets did. Studying a comet is like opening a treasure box.

In a few weeks, the mission will send its final images and data, and on September 30, 2016, the orbiter will do a slow crash landing on the surface of the comet. Its last messages should contain some very high-resolution images and data. You can follow the Rosetta mission at the ESA Website for the mission and track the spacecraft’s final days and weeks.

Rosetta: the Executive Summary

It’s been an amazing couple of years. Sure, we see what the comet’s surface looks like with its icy plains, boulders, and rocky inclusions. However, Rosetta’s chemical analysis on the comet’s ices and dust reveal information about the comet’s origins in the early epochs of the solar system’s formation. It also shows that the comet contains ingredients crucial to the formation of life. Mind you, Rosetta didn’t find life. However, uncovering the ingredients of life tells an important story. What did it find? Rosetta detected the amino acid glycine as well as the element phosphorus in the comet’s ices. These are key elements in our DNA and cell structures.

Comets as a Source of Water?

Another question astronomers wanted to answer was “Did Earth’s water come from comets?” Rosetta showed that the comet’s water chemistry is slightly different from Earth’s water. That means that ocean water on our planet didn’t all come from comets like 67P. Understanding where Earth’s water came from is still a big question in planetary science, and now astronomers are looking at other comets and asteroids for keys to the mystery.

I’m looking forward to the last images and data from Rosetta. I’m sure many comet fans, scientists, and graduate students are, too. There’s enough work in the treasury of information the spacecraft sent back to keep whole teams busy for years. In the end, even though Rosetta will no longer be working, its work WILL live on. That’s a major legacy for any mission!

comet, Comet 67P/Churyumov-Gerasimenko, comet dust, rosetta, rosetta spacecraft

Snake Eyes on a Comet

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Weird-looking Jets from Comet 67P Tell Tales of Interior Activity

This image of Rosetta’s comet taken on April 25, 2015 from a distance of approximately 93 kilometers (57 miles) shows clearly distinguishable dust jets persisting after nightfall. (Click image for a larger view.) ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The Rosetta Mission’s OSIRIS camera team released an image of jets blasting out from beneath the dusty surface of Comet 67P/Churyumov-Gerasimenko. The instant I saw the image, the jets reminded me of fangs on an alien snake or laser-like eyes on some strange sci-fi monster (how’s that for some Monday-morning pareidolia?). Actually, the truth is far more interesting than fiction.

What we’re looking at here is what happens when the Sun warms a comet. It’s a view of two jets on the side of the comet that will shortly be in darkness. And therein lies an interesting suggestion about jet activity on 67P. All along, since Rosetta arrived at the comet, we’ve been getting treated to increasing amounts of jet activity as 67P gets closer to the Sun and gets heated up. But, until recently, the jets were only active on the daylight side of the comet. Now, they’re persisting after sunset, and showing up prior to sunrise. So, what has changed?

The answer is pretty simple: as the comet gets closer to the Sun, its activity is increasing. The OSIRIS team suggests that the comet can store heat beneath the dusty crust, and the deeper layers remain warm quite a while after sunset and after the surface cools. This isn’t a new idea, since other comets have shown similar post-sunset activity, but this is the first time that astronomers have been able to get a good, high-resolution look at post-sunset jets on a comet. It’s the kind of detail that will help comet scientists understand their targets better.

Comet 67P has its closest approach to the Sun on August 13, 2015, and the Rosetta spacecraft will be tracking right along with it through this incredibly busy (and somewhat dangerous) time. For some comets, perihelion passage can break them apart. Comet 67P may not face as much danger as sun-grazing comets that come too close to the Sun. That’s because the closest it will come to the Sun is 186 million kilometers (115 million miles). Earth is 150 million kilometers (93 million miles) away, so that puts the comet’s perihelion distance at outside the orbit of Earth. Still, the comet should show quite a bit more activity, which the spacecraft will be documenting along the way. Stay tuned!