Visiting Vesta and Ceres

The Dawn spacecraft has found a lot of surprises at Vesta and Ceres. Debra Buczkowski
a geologist and planetary scientist at the Johns Hopkins University Applied Physics Lab, gave a talk recently at the Museum of Flight discussing some of the findings from the mission.

Buczkowski

Dr. Debra Buczkowski, a geologist and planetary scientist at the Johns Hopkins University Applied Physics Lab, spoke about the findings of the Dawn mission to Vesta and Ceres recently at the Museum of Flight. (Photo: Greg Scheiderer)

Vesta was Dawn’s first stop, entering orbit around the asteroid on July 15, 2011. Scientists expected to find volcanoes on Vesta. Buczkowski explained that this expectation traces back to meteorites found on Earth that are know to be from Vesta. These are known as HEDs: “howardite–eucrite–diogenite.” These closely resemble igneous rocks found on Earth, and those are made from volcanic activity. But the volcanoes aren’t there.

Before Dawn arrived at Vesta the Hubble Space Telescope showed that Vesta wasn’t spherical, but rather was significantly flattened out at its south pole. Scientists speculated that this was because of an enormous impact, and that proved to be correct. Dawn observed a huge impact crater, now called Rheasilvia Basin, the rim of which is almost as wide as Vesta itself.

“It really should have broken the asteroid apart,” Buczkowski said of the impact that created the basin, which has a huge central peak. Dawn also found a second impact crater, Veneneia Basin, which is almost as large.

Another surprise finding from Dawn is that Vesta is fully differentiated.

“Most of the asteroids are just kind of chunks of rock with one kind of rock all the way through,” Buczkowski explained. “Not Vesta; Vesta actually has a core, it has a mantle, and it has a crust.”

Vesta’s core is about half the diameter of the asteroid itself, about 220 kilometers.

“This is probably why Vesta did not fall apart when the Rheasilvia Basin formed, because it has this huge, massive core,” Buczkowski said.

The surface of Vesta was found to have lots of fractures, features larger that Earth’s Grand Canyon that look like faults. Buczkowski said they did a lot of computer modeling to see if an object the size of Vesta with a core the size of Vesta’s could develop fractures on the crust.

“The stresses that result from that huge impact kind of get redistributed because of the giant core,” she said of the findings. “Instead of being focused around the crater, they move to the equator and fracture at the equator. If we do this same model without the giant core, there’s no fracturing at the equator. So it’s because of the giant core that we have these huge fractures.”

Buczkowski said that was a little disappointing because they were hoping for volcanoes or magma-driven geology. While they didn’t find volcanoes, there is evidence of moving magma that didn’t break through to the surface. Rather, it pushed some of the surface upward, forming mounds.

On to Ceres

Dawn departed Vesta in September 2012 after spending about 14 months in orbit. As Dawn approached the dwarf planet Ceres there was much speculation about extremely bright spots on its surface that were found in Hubble images. Other observations had detected water vapor on Ceres. Since Ceres is relatively large but not dense, scientists were expecting to find ice. But there was more rock and less ice than anticipated. What they did find, Buczkowski said, was evidence of volcanism.

Occator crater

This image from NASA’s Dawn spacecraft shows Occator Crater on Ceres, with its signature bright areas. Dawn scientists have found that the central bright spot, which harbors the brightest material on Ceres, contains a variety of salts. (Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

“We’re not expecting magma on Ceres,” she said. “Ceres isn’t dense enough for the kind of magma that we’re used to here on Earth, made out of silicate rocks. This is something called cryomagma; it is basically ice with a little bit of rock.”

The biggest and brightest of the bright spots, named Cerealia Facula, is in the crater Occator. Many of the craters on Ceres are fractured, even on the crater floors, and the many bright spots on Ceres are associated with these fractures.

“What it’s looking like is that we’re having cryomagmatic activity underneath (Occator) crater,” Buczkowski said, “and what’s coming up out of these fractures is a pyroclastic spray, and the water, the volatiles in that, is sublimating away and all it’s leaving is the sodium carbonates.” Those are the bright spots we see all over Ceres.

Dawn also found that Ceres is covered in ammoniated phyllosilicates.

“Ammonia is interesting,” Buczkowski explained. “We don’t expect to find ammonia this close to the Sun, it’s usually something that’s found further out in thhe solar system.” They’re still studying whether Ceres may have formed further from the Sun and migrated in, or if the ammonia somehow made its way to Ceres from the outer solar system.

It turns out that Ceres had quite a few volcanoes, though most of them have now collapsed. There’s one that hasn’t, known as Ahuna Mons, that stands about five kilometers tall. It’s a cryovolcano.

“The volcano that we thought would be on Vesta is on Ceres,” Buczkowski noted. Ahuna Mons may be younger than the others, and also may collapse over time.

Like Vesta, Ceres was found to be differentiated, though only partially so.

“There’s a rocky core, there’s a volatile-rich mantle, and there’s a muddy slurry, a mud ocean” below the crust, Buczkowski said.

Dawn at Ceres and VestaCeres is now considered a dwarf planet, while Vesta still has asteroid status because of its lopsided shape from the giant impact. Buczkowski figures Vesta deserves dwarf-planet status, too. Whatever you call them, she thinks they’re fascinating to study because they’re kind of a bridge between the asteroids and rocky planets.

“These are more involved bodies than just plain, old asteroids,” Buczkowski said. “They’re not just chunks of rock floating in space. They’re actually like little mini-planets. They’ve got a lot of planet-like properties.”

Though they’re pretty small, they can teach us a lot.

“They’re interesting to us because they tell us a lot about how Earth and the other planets formed,” Buczkowski said. “Studying these little protoplanets we actually are looking back to the beginning of the solar system.”

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Calendar: Watch and hear a lecture from Adler

There’s a full Moon on Saturday and Daylight Saving Time ends on Sunday. Maybe that’s why the astronomy calendar is a little sparse this week!

Are we alone in the universe?

Thousands of exoplanets have been discovered over the past two decades. Dr. Lisa Kaltenegger, Director of the Carl Sagan Institute at Cornell University and an associate professor in Cornell’s astronomy department, will discuss these discoveries during a lecture at 5:30 p.m. Friday, November 3 at Adler Planetarium in Chicago. You don’t have to be in the Windy City to attend; the lecture is part of the bi-annual Kavli Fulldome Lecture Series and will be live streamed to the Pacific Science Center’s Willard Smith Planetarium! It’s part of the center’s on-going Science in the City lecture series. Kaltenegger will explore how we can determine which exoplanets might be suitable for life and cover techniques and missions that could detect life on these faraway worlds.

Tickets are $5, and free to science center members. Space is limited, so advance tickets are recommended.

Club meetings

The Spokane Astronomical Society will meet at 7:30 p.m. Friday, November 3 at the planetarium at Spokane Falls Community College. The guest speaker had not been published as of this writing.

The Seattle Astronomical Society will offer one of its new members orientation sessions at 2 p.m. Sunday, November 5 at the Theodor Jacobsen Observatory on the University of Washington campus in Seattle. While the title calls out “new members,” prospective members are welcome as well. It’s a good time to find out what the society has to offer—and sign up!

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Astro Biz: Moondrops nuts

MoondropsMany businesses, products, and places have names rooted in space and astronomy. We’re featuring one every Tuesday on Seattle Astronomy.

This week’s Astro Biz is Moondrops Bavarian Roasted Nuts. Moondrops is based in Vancouver, Washington and can typically be found at the Saturday Market in Portland, Oregon. We spotted their booth at the Wine Country Eclipse event at the Polk County Fairgrounds in Rickreall, Oregon the weekend before the total solar eclipse in August.

Moondrops offers a variety of almonds, cashews, walnuts, and hazelnuts roasted in cinnamon, sugar, and other goodies.

More info:

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APOD: more than just pretty pictures

The Astronomy Picture of the Day is more than just a pretty photo. In fact, each of the featured images may well have more than a thousand words packed into it. You just need to drill down deeper into the site.

John McLaren, a NASA Solar System Ambassador and treasurer of the Seattle Astronomical Society, gave a presentation about APOD at the society’s meeting last week. He said the key to finding a wealth of information about celestial objects is dragging your eyes away from the pretty pictures long enough to notice the explanation of the photo and, more importantly, the submenu below it. McLaren uses this information when preparing presentations about astronomy for various groups.

“You can build a more complete story,” he explained. “There are good links here for education, for outreach, and home-schooling groups.”

You’ve probably noticed that the explanations of the photos use plenty of links to further information. Below the explanation there’s typically a set of “more on” links about objects or content. The real prize, though is in the index, a fully searchable listing of what’s on the APOD site.

That’s a lot of stuff. McLaren noted that the site was started by Robert Nemiroff and Jerry Bonnell when both worked at the Goddard Space Flight Center. The first posts were in June of 1995, and there have been more than eight thousand of them since. McLaren pointed out that when you look at the site, it is very 1995. There’s no flash or fancy moving menus. It’s pretty straight HTML, and the authors figured that changing things would run the risk of breaking a zillion links to APOD information.

Earth from Apollo 17

The Earth from Apollo 17
Picture Credit: NASA, Apollo 17, NSSDC

They don’t update the photos published, either. Clicking on each photo gives you the best version of it that they have. The one at left, a photo of Earth taken from Apollo 17 in 1972, was posted in the first week of APOD’s operation. When McLaren showed this photo on the big screen during his presentation, there was some laughter about its low resolution. He reminded us that in 1995 we were probably dialing in to the Internet with a 2400 baud modem, and that wouldn’t deliver the high-res goods in the manner to which we’ve become accustomed in our broadband world.

Click the “archive” link on each page and you’ll find a long scroll, day by day, of every APOD ever. The “index” link takes you to a menu of stars, galaxies, and nebulae, solar system objects, space technology, people, and the sky. Clicking on these will give you a handful of “editors’ choice” photos they consider to be the most educational on the chosen subject.

McLaren found this photo, the APOD of October 20, 2002, of the space shuttle docked with the Russian Mir space station in 1995. It made him wonder who took it. Was it the first known selfie?

Shuttle and Mir

The Space Shuttle Docked with Mir. Credit: Nikolai Budarin, Russian Space Research Institute, NASA

“Since it was the first docking, they wanted to get good information about how the two spacecraft functioned together,” McLaren explained. “So one of the Soyuz crews on Mir actually undocked their Soyuz spacecraft, did a fly-around, and observed the combination.” All of that was found by following the links on the photo page.

Astrophotographers who aspire to be published on APOD may well wish to check out its index of Messier objects. McLaren points out that many of the objects in the index are represented by numbers, not pictures.

“They don’t have photos of all the Messier objects posted yet, so if you submit a good color picture of them you may get your photo as the astronomy photo of the day,” he noted, which could lead to fame and fortune or at least bragging rights.

The search engine for the index is useful. Type in “Saturn rings” and it will find 200 items.

“There’s a wealth of information in there if you’re looking for something,” McLaren said.

So the next time you’re checking out the Astronomy Picture of the Day, remember that there’s a whole lot of knowledge lurking beneath those gorgeous photos.

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Calendar: spooky action

Astronomy on Tap Seattle returns for its October event this week, and local planetaria get into the Halloween spirit.

Hitchhiker’s guide to the galaxies

AOT Oct 25Astronomy on Tap Seattle will be all about galaxies when its monthly meeting convenes at 7 p.m. Wednesday, October 25 at Peddler Brewing Company in Ballard. This month’s speakers will be Dr. Jennifer Sobeck, who will discuss her research on the evolution of our galaxy in her talk “A Hitchhiker’s Guide to the Galaxy: Bumming Around the Milky Way,” and Grace Telford, whose talk “A Whirlwind Tour of Galaxies: the Tiny, the Gigantic, and Everything in Between” will zoom out and take a census of other galaxies.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington, and features informative talks, astronomy-themed trivia contests, excellent prizes, and beer. Bring your own chair to create front-row seating.

Star parties this week

There are several free public star parties on the schedule for this week.

The monthly Covington Community Park star party is set for 8 p.m. Friday, October 27 at the park on 240th in Covington. The event is a joint effort of the Seattle, Boeing Employees, and Tacoma astronomical societies. The Seattle Astronomical Society will hold star parties at 7 p.m. Saturday, October 28 at two locations: Green Lake in Seattle and Paramount Park in Shoreline. These events can be cancelled in case of inclement weather, so watch the website or social media of the Seattle Astronomical Society.

The Tacoma Astronomical Society plans one of its public nights for 7:30 p.m. Saturday, October 28 at the Fort Steilacoom campus of Pierce College. The indoor program is a Halloween special. Stargazing will happen if the skies are clear.

Spooky action in planetaria

Area planetarium operators get into the Halloween spirit with holiday-themed shows this weekend. The Washington State University planetarium in Pullman will offer a program titled Cosmic Spooks, featuring creepy illusions in the sky, disturbing constellation mythology, and a dose of real danger. Shows are at 7 p.m. Friday, October 27 and at 5 p.m. and 7 p.m. Sunday, October 29. Tickets at the door are $5, cash or check; no credit cards.

It’s the last weekend for the Haunted Night Sky show at the Pierce College Science Dome. The tour to spooky places in the universe is geared toward kids ages 3–12. Showtimes are 12:30 p.m. and 2 p.m. on Saturday, October 28. Adults get in for free but kids have to pay $6. Tickets are available in advance online.

Scout for future events on the Seattle Astronomy calendar.

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Calendar: Six NW astro-club meetings this week

Orbit Around October continues at the Museum of Flight, and there are a slew of astronomy club meetings on the calendar for this week.

Orbit

Orbit Around OctoberThe Museum of Flight continues its spacey month with a visit to Ceres at 2 p.m. Saturday, October 21. Johns Hopkins University Applied Physics Lab participating scientist Debra Buczkowski will talk about the discoveries of NASA’s Dawn mission to the giant asteroid Vesta and dwarf planet Ceres. Buczkowski will discuss what we learned about Vesta and Ceres, and how this helps us understand the formation of bodies in the asteroid belt. Free with museum admission.

Star party in Oak Harbor

The Island County Astronomical Society plans its monthly star party in Fort Nugent Park for around dusk on Friday, October 20.

Haunted night sky

The popular planetarium show Haunted Night Sky continues on Saturdays through October at the Pierce College Science Dome. Show times for October 21 are 12:30 p.m. and 2 p.m., and the program runs about 45 minutes. The show is designed for kids ages 3–12. Tickets are $6 for children, free for adults, and are available online.

Astronomy club meetings

There are half a dozen astronomy club meetings in the region this week:

Mark your calendar

The next Astronomy on Tap Seattle event is set for 7 p.m. Wednesday, October 25 at Peddler Brewing Company in Ballard. The theme will be “A Hitchhiker’s Guide to the Galaxies” and the evening will feature talks about galaxy types, formation, and evolution. Plus beer and astronomy trivia.

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Seeing the invisible and finding aliens using polarimetry

The topic line for last week’s gathering of Astronomy on Tap Seattle was What the Hell is Polarimetry?, and it seemed that a significant portion of the audience at Peddler Brewing Company in Ballard shared the question.

UW postdocs Jamie Lomax and Kim Bott explained that when light starts from its source the oscillation of its wave—its “wiggle”—goes in all directions until an interaction with something makes it polarized.

“That just means that it’s wiggling in one direction,” Lomax noted. “There’s a preferred plane for that wiggle to happen in, and in polarimetry what we’re doing is measuring that preferred plane and we’re looking for light that has been polarized.”

“It can help you figure out the shape of things without having to resolve the object,” Bott added.

Polarimetry and massive stars

Lomax studies massive stars and has found use for polarimetry in her work. She gave a talk titled, “Seeing Invisible Circumstellar Structures.”

Jamie Lomax

Jamie Lomax

“The holy grail for us in massive star research is to be able to take a massive star at the beginning of its lifetime, figure out how massive it is,” Lomax said, “and map out what its life is going to look like and figure out what supernova it’s going to end its life as.”

“It turns out that is really hard, and it’s complicated by the fact that most massive stars are probably in binary systems,” she added. Since about two-thirds of massive stars are part of a binary system, one might expect that two-thirds of core-collapse supernovae would be from such systems.

“There’s a problem, and that is we’ve only seen maybe two or three core-collapse supernovae where we have evidence that suggests that it’s come from a binary star,” Lomax said.

Part of the problem, she said, is that we don’t yet know enough about the evolution of binary star systems.

“We can try to hammer out the details of how that mass is transferring between the two stars and when the system is losing material to try to figure out how that effects its future evolution,” Lomax said. “Once we start answering questions like that we can start to tease out why we aren’t seeing all of these binary supernovae we think we should be seeing.”

Lomax talked about the star Beta Lyrae, a binary system. The primary star in the system is losing mass that gets gobbled up by the secondary. This transfer of mass also forms a thick accretion disk of gas around the secondary—so thick light from the actual star can’t get through. There’s also evidence that there are jets shooting out of the system, but we don’t know where they are.

“These are all features that we can’t see very well,” Lomax said. “We can’t see the mass transfer stream between the two stars, we can’t see the jets.”

Here’s where polarimetry comes in. If a star is surrounded by a cloud of gas or dust that is circularly symmetrical, when the starlight interacts with that material the light becomes polarized, and the wiggles line up tangentially with the edge of the disk. If the cloud is elongated in some way, the wiggles form in a “preferred” direction.

“That preferred wiggle direction is 90 degrees from the direction of the elongation of the disk, so you can back out geometric information pretty quickly,” Lomax said. “Just by looking at how the light is wiggling I can tell you how the disc is oriented on the sky.”

Lomax figures that if you don’t do polarimetry you’re throwing out free information.

“You can see invisible things—to you—and that gives you extra information about what’s going on in different systems.”

Exoplanets and aliens

Bott’s talk was titled “The Polarizing Topics of Aliens and Habitable Planets.” She studies exoplanets and said polarimetry comes in handy.

“Stars don’t produce polarized light, which is really great if you’re trying to look at something dim like a planet,” she noted. The polarimeter will simply block out the starlight. There are then a number of things that might be spotted on the planet:

  • Glint from an ocean
  • Rayleigh scattering
  • Clouds and hazes
  • Rainbows
  • Biosignatures of gases in an atmosphere
  • Chiromolecules
Kim Bott

Kim Bott

These can help astronomers characterize a planet, judge its potential habitability, and even determine if life might already be flourishing there.

Bott said that polarimeters that are sensitive enough to study planets are a recent advance, and they’re studying big, bright planets to get the hang of it. Looking for rainbows can be revealing about liquids in the atmosphere of a planet.

“The light will bend in the droplets at a slightly different angle depending what the droplet is made out of,” Bott said, so they can tell whether its water, methane, or sulfuric acid.

“We’re trying to create these really robust models that will take into consideration polarized light from Rayleigh scattering in the atmosphere as well as from rainbows,” Bott said, “and if you have a planet where you can see the surface you’d be able to see the signature from glint as well.”

Since different substances bend light at different angles, we can also learn a lot by watching closely as planets move through their phases as they orbit their host stars.

“On Earth we have light going from air and bouncing off of H2O water,” Bott said. “That’s going to produce a maximum in polarized light at a different angle than on, say, Titan, where you have light going from a methane atmosphere and then bouncing off of a hydrocarbon ocean.”

“We can actually, in theory, tell what the ocean and atmosphere are made out of by looking at where, exactly, in the orbit we see this glint,” Bott explained.

As for aliens, life requires more complex molecules, chiromolecules, that are “wound” in a certain direction, like our own DNA. Such molecules would produce circularly polarized light, which if detected could be a sign that such molecules exist on the planet.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington. It’s next gathering is scheduled for October 30 at Peddler Brewing Company in Ballard.

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