Space Oddities: Comet With an Aurora and Asteroid With Foreign Rocks

This is Major Tom to Ground Control
I’m stepping through the door
And I’m floating in a most peculiar way
And the stars look very different today

— Space Oddity (David Bowie)

Hey, Ground Control, you’re not going to believe this, but I think I see a comet with a strange aurora around it. That’s not right, is it? And over there is a weird-looking asteroid, but what’s really weird is that the rocks on the surface don’t match the other ones … like maybe they came from another asteroid. Weird, right? Planet Earth still looks blue … that’s a relief. Is there anything I can do? Yes, I took my protein pills. There’s nothing I can do? Maybe I’ll write a song.

David Bowie told us that space is full of oddities and he was certainly right about that. This week, NASA’s OSIRIS-REx spacecraft spotted some strange rocks on the surface of asteroid Bennu that appear to have come from someplace else, while a new analysis of data collected by the Rosetta spacecraft while it orbited Comet 67P Churyumov-Gerasimenko (67P/C-G) shows the comet glowing with a far-ultraviolet auroral radiation. Did THEY take their protein pills?

Comet 67P/C-G

“We found six boulders ranging in size from 5 to 14 feet (about 1.5 to 4.3 meters) scattered across Bennu’s southern hemisphere and near the equator. These boulders are much brighter than the rest of Bennu and match material from Vesta.” (Daniella DellaGiustina of the Lunar & Planetary Laboratory, University of Arizona, Tucson)

 

“Our leading hypothesis is that Bennu inherited this material from its parent asteroid after a vestoid (a fragment from Vesta) struck the parent. Then, when the parent asteroid was catastrophically disrupted, a portion of its debris accumulated under its own gravity into Bennu, including some of the pyroxene from Vesta.” (Hannah Kaplan of NASA’s Goddard Space Flight Center in Greenbelt, Maryland)

Bennu

It’s hard out there for an asteroid (2005 non-Bowie song reference), as these two space scientists explain in a NASA press release announcing the discovery of extremely bright boulders on Bennu. Using the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) instrument, they matched the repflected light to that coming from the mineral pyroxene, which is similar to what is seen on Vesta and the Vestoids – not an early all-girl band but fragments blasted by an impact off of an earlier, larger Vesta. In the tightly-packed asteroid belt between Jupiter and Mars, these impacts are not unusual, or as NASA more musically puts it:

“This indicates many asteroids are participating in a complex orbital dance that sometimes results in cosmic mashups.”

Meanwhile, on Comet 67P Churyumov-Gerasimenko (a Jupiter-family comet originally from the Kuiper belt that was orbited by the European Space Agency’s Rosetta mission, which dropped a lander on its surface before crashing into it two years later), researchers taking a fresh look at the glow around the comet have come to a new conclusion about its cause.

“Initially, we thought the ultraviolet emissions at comet 67P were phenomena known as ‘dayglow,’ a process caused by solar photons interacting with cometary gas. We were amazed to discover that the UV emissions are aurora, driven not by photons, but by electrons in the solar wind that break apart water and other molecules in the coma and have been accelerated in the comet’s nearby environment. The resulting excited atoms make this distinctive light.”

In fact, Dr. Joel Parker of the Southwest Research Institute (SwRI) says the glow is an aurora – something never seen around a comet until now. While they have been visible around planets and moons, they weren’t expected around comets because they lack a magnetic field to interact with the charged particles in solar wind, causing them to glow in auroras. In the case of 67P/C-G, it was the comet’s coma – the envelope of gas surrounding it – which was excited by the solar particles and made to glow in an ultraviolet light.

Both of these discoveries are further proof that the universe is full of space oddities and the study of data from space missions should never end, just like the playing of David Bowie’s music.

There’s something we all can do.

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