White spots on Ceres may be salt

The first big surprise as the Dawn spacecraft was approaching the dwarf planet Ceres earlier this year were bright white spots on its surface. Now that Dawn has been orbiting Ceres for six weeks, a theory has emerged about what the spots are: salt.

Dr. Tom McCord, a planetary physicist who is co-investigator on
the Dawn mission, spoke about the exploration of Ceres Saturday
during an Astronomy Day event at the Pacific Science Center
in Seattle. Photo: Greg Scheiderer.

Dr. Tom McCord, a co-investigator on the Dawn mission and director of the Bear Fight Institute, a research organization based in Winthrop, Wash., spoke at an Astronomy Day event Saturday at the Pacific Science Center in Seattle. Here’s why he thinks the spots could be salt.

McCord explained that Ceres is differentiated: it has a rocky core, a water-ice mantle layer, and a dirty crust. He noted that they’ve learned a lot from the early photographs.

“There’s a lot of evidence of activity; many craters, an older surface, but not as old as the object, so something obliterated the craters from early on,” McCord said. “Distorted features, so the surface had to have been warped.”

“There are domes, things pushing out from the inside,” he continued, “and bright spots that suggest that material from inside has come to the surface in some sort of volcanism.”

In addition, McCord explained that ground-based telescopes have detected water vapor that comes and goes in the area of Ceres. Liquid water from the interior of Ceres may be being ejected to the surface, where it wouldn’t last long.

This image was taken by NASA’s Dawn spacecraft of dwarf
planet Ceres on Feb. 19 from a distance of nearly 29,000
miles (46,000 kilometers). It shows that the brightest spot
on Ceres has a dimmer companion, which apparently lies
in the same basin.
Photo: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

“What that would do is leave a residual salt deposit, so these bright spots could be salt deposits that accumulated around vents—volcanos—where the water is coming through,” McCord speculated.

He stresses that the work on data from Ceres is still in its early phases, joking that, “We scientists don’t know entirely what we are seeing.”

McCord said the evidence of geological activity has been the most interesting finding so far at Ceres.

“It has been active and may well still be active today,” he said. “That’s exciting to a physicist because you really want to know whether these processes that you conjure up in your models really have happened and, we hope to learn, to what extent and over what time scale.”

Ceres is a great target for study because it may hold clues to how planets form. It is the only dwarf planet in the inner solar system and is the largest object in the asteroid belt. With a diameter of 590 miles, it’s about as big as Texas.

“This is a very large small planet,” McCord said. Ceres comprises about a third of the mass of all objects in the asteroid belt.

The Dawn spacecraft is unique, according to McCord.

“It is the only interplanetary spacecraft that uses ion propulsion, and that is the only reason we are able to orbit two different objects in the outer solar system and still have enough fuel to go on,” he said. Dawn launched in 2007 and studied the asteroid Vesta for 14 months in 2011 and 2012 before heading to Ceres.

“Dawn is really a pathfinder for this kind of multiple-object extended exploration,” McCord said.

Dawn will be collecting data at Ceres for another year to 18 months. McCord said the spacecraft has four momentum wheels and needs three of them to hold itself in stable position. However two of the wheels have failed, so mission scientists are using the craft’s thrusters as a substitute. The hydrazine fuel will eventually run out, and Dawn will tumble about in a stable orbit around Ceres for a long, long time.

Beyond pretty pictures; amateurs contributing to astronomical science

Ralph Megna is an amateur astronomer only in the sense that he doesn’t get paid for his work. But he’s making some major contributions to the science and working with the big guys.

Megna is a co-founder of the nonprofit Center for Solar System Studies, an amateur organization that is building several observatories in Landers, California, in the Mojave Desert east of Riverside. He’s a long-time astronomy enthusiast, but a real estate developer by daytime profession. He and several colleagues at the Center, CS3 for short, recently wrapped up a project to provide some critical data for NASA’s DAWN mission to Vesta and Ceres. This is somewhat akin to a hobbyist who is pretty good at softball suddenly being asked to play second base for the St. Louis Cardinals.

Ralph Megna of the Center for Solar System
 Studies is an amateur astronomer, but he and CS3
colleagues are doing real work with NASA.
Megna spoke Sunday at the annual banquet
of the Seattle Astronomical Society.
Photo: Greg Scheiderer.

Megna talked about the experience Sunday night as the keynote speaker at the annual banquet of the Seattle Astronomical Society. The involvement with NASA came because, as DAWN approached Vesta, it couldn’t make much sense out of data collected by a framing camera, a key part of the craft’s navigation.

“Their own stuff turned out to be crap,” Megna said of NASA’s data on Vesta. They knew of the work being done at CS3 and turned to them get better information about Ceres.

“We were recruited by NASA to collect some specialized photometric data,” Megna said. CS3’s Earth-based telescopes and cameras made precise observations of Ceres and its phase angle, rotation, albedo, and the like. They imaged the asteroid between last September and earlier this month. The data will help DAWN better navigate its way when it leaves Vesta and heads for Ceres this summer.

“We were told by NASA that this was the first time in NASA history that it had turned to amateurs to provide it with mission-critical data in order to guide an interplanetary spacecraft,” Megna said. “We were pretty proud to be asked to do that.”

Megna’s talk was titled “Beyond Pretty Pictures: How Amateur Astronomers are Making Discoveries & Changing Solar System Science.” He noted there’s been an explosion in interest in astrophotography in recent years.

“We’ve now probably passed the one billionth picture of M42,” Megna joked about the Orion Nebula, one of the most photographed celestial objects. Part of their mission at CS3 is to push the envelope.

“We’re exploring some new territory with respect to the contributions that amateur astronomers can make to real science in astronomy,” he said, adding that the main thing that makes those contributions possible is relatively inexpensive and readily available technology, especially scientific-quality CCD cameras.

“That single thing has really leveled the playing field between us and professionals and has made it possible for us to make real contributions to real science,” Megna said. Amateurs are making amazingly precise observations of variable stars, finding supernovas, monitoring planets, tracking exoplanet transits, and doing his thing—asteroid photometry.

“All of these things are now possible because, frankly, the technology has become accessible and affordable to amateur astronomers,” he said. “The kind of information that amateurs are collecting gets sucked up by the computer models that are being created by professional astronomers and astrophysicists. This has led to some exciting new theories on the evolution of the solar system.”

Chief among these is the Nice model of solar system evolution, which proposes that the gas giant planets were once much closer to the Sun, but migrated out, flinging lots of material clean out of the solar system in the process. Megna said much of the data that the model crunched was collected by amateurs.

Discoveries of binary asteroid systems and measurements of asteroid shapes and orbital dynamics are cool and important, but Megna said that’s not really what drives him.

“I can’t tell you what a rush it is to watch that light curve get composed by the computer on the screen and know that I am the first person in human history to know what the length of a day is on another celestial body,” he explained. “This may be a footnote to a footnote to a footnote in science, but it is a moment of discovery.

“This moment of personal discovery is an incredibly important motivator to what I do,” Megna added. “It hearkens to the notion of being an amateur astronomer. The origin of the word amateur is to love; I do this because I love to do it.”

He’s pretty good at it, too.