Despite the arrival at the planet of the Dawn space craft over a month ago, NASA scientists are nowhere nearer to finding an explanation for this unusual phenomenon than they were before.
It was expected that more detailed information from the space probe would resolve the riddle of the Ceres lights, but, in fact, the latest data has now left scientists even more puzzled.
New infrared images of the dwarf planet’s surface seem to show that the two principal light centers, called Spot 1 and Spot 5, “behave distinctly differently,” said Federico Tosi, who works on Dawn’s Visible and Infrared Mapping Spectrometer (VIR).
Infrared images released at a meeting of the European Geosciences Union in Vienna on April 13, show a strange discrepancy between Spot 1 and Spot 5, which scientists can’t explain. Spot 1 is colder than its immediate surroundings, while Spot 5 isn’t. Why this is so, no one can say.
Phys.org says that to the human eye, Ceres looks like a “dark and brownish” ball with both white spots clearly visible. However, in thermal images, Spot 1 becomes a dark spot on a reddish ball, indicating it was cooler than the rest of the surface.
Spot 5, which is the brightest does not show up at all in the infrared images. Why two similar lights show such differences, can’t yet be explained.
Scientists had believed that the spots would provide key evidence of the planet’s chemical and physical ID, and confirm theories that Ceres is a water-rich planetary “embryo”—a relic from the birth of the Solar System some 4.5 billion years ago, says Phys.org.
Until now, scientists have hypothesized that the spots might be ice found at the bottom of a crater or alternatively ice plumes thrown up by water volcanoes or ‘cryovolcanoes.’
The “ice theory,” however, doesn’t hold water (pun intended), since the planet’s surface is just a little too close to the sun for stable ice to form, says Tosi.
Moreover, in the new images, taken while the planet goes in and out of sunlight, the spots are still visible at the edge of Ceres, which would mean they couldn’t be ice inside a basin, but must be something quite high above the surface.
Nature quotes Andreas Nathues, a planetary scientist at the Max Planck Institute for Solar System Research in Göttingen, Germany, who says, “What is amazing is that you can see the feature while the rim is still in the line of sight,”
Nathues leads the team for one of the Dawn cameras and displayed the images at the Lunar and Planetary Science Conference in The Woodlands, Texas on 17 March. Nathues told the meeting in Texas that; “The big question is whether Ceres has an active region — or more than one.”
The only other theory on the block is that the spots are “hydrated minerals,” which is water absorbed by minerals, rather than taking on a pure ice form. But this too cannot be confirmed.
The New Scientist quotes Tosi, who cautions,
“The current indication is there might be bright spots on the surface of Ceres behaving differently. Before invoking cryovolcanoes or something strange going on, we have to be prudent and rule out the easy possibilities.”
On its website yesterday, NASA admitted that “The origins of Ceres’ bright spots, which have captivated the attention of scientists and the public alike, remain unknown.”
What is also puzzling scientists is that Ceres should have a similar number of craters and of a similar size to those found by the Dawn spacecraft on the neighboring asteroid, Vesta – but they just aren’t there!
Christopher Russell who leads the Dawn mission said,
“When we compare the size of the craters with those we see on Vesta, we are missing a number of larger craters. That’s something we’ve got to learn more about when we take the next stage of science data.”
Scientists are hoping the riddle of the bright lights can be resolved, when the Dawn craft moves into a permanent orbit around Ceres on April 23rd, and closer, more detailed images are sent back.
