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Beta Pictoris has Comets

An artist's concept of comets around the star Beta Pictoris. The HARPS instrument at ESO’s La Silla Observatory in Chile was used to make the most complete census of comets around another star ever created. A French team of astronomers has studied nearly 500 individual comets orbiting the star Beta Pictoris and has discovered that they belong to two distinct families of exocomets: old exocomets that have made multiple passages near the star, and younger exocomets that probably came from the recent breakup of one or more larger objects.  Courtesy ESO/L. Calçada

An artist’s concept of comets around the star Beta Pictoris. The HARPS instrument at ESO’s La Silla Observatory in Chile was used to make the most complete census of comets around another star ever created. A French team of astronomers has studied nearly 500 individual comets orbiting the star Beta Pictoris and has discovered that they belong to two distinct families of exocomets: old exocomets that have made multiple passages near the star, and younger exocomets that probably came from the recent breakup of one or more larger objects. Courtesy ESO/L. Calçada

The southern hemisphere star Beta Pictoris has been one of the great “go to” places for exoplanet stories in the years since it was discovered to have a ring of debris around it by the IRAS satellite in 1983. To be specific, IRAS found excess infrared emission around the star, which indicated the presence of the disk. The disk has been imaged from ground-based observatories, and studied by Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer (FUSE), among others. The Hubble studies showed that Beta Pictoris has no one, but two disks of material, and it’s very likely that the materials in this disk are in the early stages of planetary formation.

In a spectacular study just released by the European Southern Observatory, astronomers using the HARPS “planet hunter” instrument at the La Silla Observatory in Chile have made a census of comets orbit Beta Pictoris. They studied about 500 of these “exocomets” and grouped them into two “families”. One is a group of old comets that have been around the star many times and have been heated and lost some of their mass. The other is a collection of young comets that are the result of the breakup of larger icy objects orbiting the star. This is the most extensive survey of comets around another star ever made and may well help us understand the role of comets in the early stages of solar system formation.

Beta Pictoris is a very young star system — only about 20 million years, which makes it an infant, as stars go. By contrast, the Sun is 4.5 billion years old, and the entire solar sysem may have looked very much like Beta Pic back when it was a baby.

The disk surrounding Beta Pictoris is filled with gas and dust, plus larger particles and planetesimals. As astronomers watched this star over the years, they noticed that the star itself would ever-so-slightly dim as something passed in front of it. The star does have a planet, but many of these dimmings did not correspond with that planet’s orbit.

What were they? It turns out that they were comets. Yes, comets can dim a star’s light as they evaporate. Their gases and dust are perfect “light traps” to capture starlight as it passes through, thus causing the star to seem just a little bit less bright for a short time. The science team studied the light to determine the types of comets the instrument detected.

So, the age of exoplanet discovery has expanded into the age of exocomet studies. And, as I recall from another news story, it joins the age of asteroidal dicovery around other stars. All of these ages not only help us understand the formation of planets and objects around other stars, but give us a fascinating look back at how our own system must have looked nearly 5 billion years ago.

No Really, Look at It!

UP close and personal with Comet 67P/Churyumov-Gerasimenko.  Courtesy Rosetta/ESA.

UP close and personal with Comet 67P/Churyumov-Gerasimenko. Courtesy Rosetta/ESA.

You haven’t ever seen anything quite like this in your life. This is one of a continuing series of very cool images taken by the Rosetta’s NavCam imager from a distance of 9.8 kilometers from the center of the comet. What you see here is a region on the “neck” that connects the two parts of the comet together. There are rockpiles, outcrops, smooth areas, and — right in the center — what looks like dunes!

Dunes?  On a comet?

That’s what many of us said when we saw this image.  On one of the Facebook comet groups I’m part of, we joked around a lot about how the “spice must flow” in an obligatory “Dune” reference, but truth to tell, we were amazed to see these. What could be causing them?  It’s not like there’s an atmosphere and heavy winds on the comet’s nucleus to contribute aeolian (wind-driven) forces to the comet (although there is small atmosphere, gravitationally bound to the comet.  See the comments to this article for a more nuanced discussion of that).

But, think about it. We’re looking at an icy object that is getting close to the Sun (and thus is outgassing material from deep inside the comet due to the effects of solar heating). It will do more of this “mass loss” as it passes through perihelion (the closest point to the Sun) in its orbit. Outgassing comes from within the comet. So, chances are very good that those dunes are close to an outgassing vent. Or, at least, that’s what I’m hypothesizing. If so, then maybe the boulders were displaced by outgassing as well.

There’s a lot to learn about this comet, and the stream of images from Rosetta’s NavCam are paving the way to a greater understanding of just how comets change as they approach the Sun.  Many thanks to the ESA folks who have been sharing images and blogging about them, and to the NavCam team for making them available. It’s WAY more than we’re seeing from the OSIRIS team (headquartered at Max Planck Institute), which has apparently holed up in an undisclosed location to study images from their Precious away from unworthy eyes. If all goes well, we may see their work in, oh, six or so months, long after the public’s attention has turned to other missions and other fantastic achievements from teams that care enough to share their science with their fellow human beings as the discoveries are happening.

In the meantime, keep an eye peeled as Rosetta prepares to launch the Philae probe to the surface on November 12, 2014. The proposed landing site, currently named “J” is the subject of a naming contest, so if you’d like to see a fancier name than a single letter, enter the contest as soon as you can.It ends at midnight GMT, October 22nd!