News in Space

The Mysterious Spots on World Ceres

On March 6th, NASA’s Dawn spacecraft arrived at Ceres—at 600 miles in diameter, the largest object in the asteroid belt—making history not only as the first spacecraft to orbit two extraterrestrial bodies but also as humankind’s first-ever visit to a dwarf planet. From a circular, polar “RC3 orbit” 8,400 miles (13,500 kilometers) above the surface, Dawn recently completed its first survey of Ceres, mapping its entire surface to a resolution of 4,200 feet (1,280 meters) per pixel, and it is now sending back high-resolution, full-disk images of what some are punnily calling “World Ceres.”

The 2,500 or so images expected from the RC3 download include our closest look yet at the mysterious bright spots inside a 57-mile wide crater. Initially detected as a single spot by the Hubble Space Telescope (HST) in 2004, the two spots were resolved as separate by Dawn from 29,000 miles (47,000 kilometers) away. (That said, astronomer-blogger Phil Plait quotes a member of the HST team who claims that the Dawn images do not show the same feature.)

Dawn’s higher-resolution view has revealed that the fainter of the two spots is actually a swarm of at least ten smaller spots blurred together by the high contrast ratio of the image. Astronomers have speculated that the spots’ brightness suggests the presence of highly reflective material such as ice, catching glints of sunlight. Other possibilities include ice-volcanoes, geysers, or salt deposits.

Presently, Dawn is in the process of descending to a closer “Survey Orbit” only 2,700 miles (4,350 kilometers) high. Thanks to the gentle thrust of its ion engine, this will take a month, arriving at the proper altitude on June 6th. From that height, camera resolution will be 1,400 feet (430 meters) per pixel and give an even better view of the surface, including the spots. Dawn will remain in this orbit for all of June, then descend to the “High Altitude Mapping Orbit” at 900 miles (about 1,500 kilometers), observing the surface with a resolution of 450 feet (138 meters) from August 4th through October 5th. Finally, late in the year, Dawn descends to the “Low Altitude Mapping Orbit,” where it will circle Ceres at a height of 230 miles (370 kilometers), with a resolution of 120 feet (37 meters). It will remain in this orbit from December 8th to the end of mission, expected to occur at the end of 2016, when the spacecraft runs out of maneuvering fuel. Then, it will remain an artificial satellite of Ceres, locked in a very stable permanent polar orbit. –Bing Quock

Salt Discoloring Europa Crust

A NASA press release this week announced that laboratory experiments indicate the dark areas across the surface of Jupiter’s moon Europa may be caused by irradiated, discolored salt from the ocean underneath its icy crust. The study was published this week in Geophysical Research Letters.

Europa’s mantle and ocean are covered by a thick ice surface, where scientists have noted dark material coating long, linear fractures and other relatively young geological features. It has long been suspected they might be caused by salts coming from ocean below, but data were limited.

To determine the composition of the dark material, a team at the Jet Propulsion Laboratory (JPL) simulated the conditions on the moon’s surface in their lab, with special consideration given to the intense radiation the world receives from Jupiter’s magnetic field.

“We call it our ‘Europa in a can,’” said Kevin Hand of JPL. “The lab setup mimics conditions on Europa’s surface in terms of temperature, pressure and radiation exposure. The spectra of these materials can then be compared to those collected by spacecraft and telescopes.”

The team used table salt (sodium chloride), along with mixtures of salt and water, in the simulation. After a few tens of hours of exposure (which corresponds to a century on Europa), the samples turned from white to a yellowish-brown, similar to color of the moon’s. Spectra taken of the samples strongly correlated to spectra taken by the Galileo mission of similar-colored regions on Europa. The longer the salt was exposed, the darker it became, leading Hand to believes the color variation may help determine the ages of geologic features and material ejected from any plumes that might have occurred.

More significantly, the findings suggest the salts are deposited as a result of interaction between Europa’s ocean and its rocky seafloor, an interaction many consider an important consideration in determining whether Europa could support life. –Elise Ricard

Farther in space and further back in time

Last month, we wrote about Hubble’s amazing contributions to space science, and last week, the telescope again proved to be the gift that keeps on giving. Within the Hubble Ultra Deep Field, astronomers havedetermined that galaxy EGS-zs8-1 is the most distant object humans have ever observed.

This galaxy lies so far away that the light we see in our telescopes has been traveling through space for nearly 13 billion years. This gives us a way to observe directly into the past and to see what the galaxy was like when the Universe was only 5% of its current age. From observations from Hubble, Spitzer, and the Keck I telescopes, scientists understand that, for a young galaxy, it grew fast. A mere 670 million years after the Big Bang, this galaxy already amassed more than one-seventh of the visible stuff that makes up our own sizeable Milky Way galaxy.

This immense infant shows a powerful hunger, too, forming stars out of plentiful hydrogen at impressive speeds. In fact, EGS-zs8-1 is showing a whopping 80 times the rate of star formation compared to the sluggish rate at which stars form in the venerable 13-billion-year-old Milky Way.

The galaxy was initially identified based on its brightness and peculiar colors. The astronomers discovered that its multitude of bright young stars influence the color of the galaxy as a whole, and when that light passes through the primordial gas, it transitions from a neutral state (mostly hydrogen, consisting of a paired proton and electron) to an ionized state (free floating protons and electrons). Seeing this change and the light from this galaxy allows an important glimpse back in time to a primordial state that has not existed for billions of years. Pretty amazing stuff! –Josh Roberts

Image(s): NASA