The first triple asteroid near Earth has been discovered.
Astronomers have found plenty of double, or binary asteroids. Triples are known to exist, too (the first triple was found in 2005).
But the system called 2001 SN263 is the closest triple, at just 7 million miles (11.2 million kilometers) from Earth.
It was originally found in 2001, but new observations with the radar telescope at the Arecibo Observatory in Puerto Rico reveal it is three gravitationally bound rocks.
The main rock is spherical and about 1.5 miles (2 kilometers) wide. Another is about half that size. The smallest is about 1,000 feet across, or about the size of the Arecibo telescope, astronomers said.
"This discovery has extremely important implications for ideas about the origins of near-Earth asteroids and the processes responsible for their physical properties," said Cornell University and Arecibo astronomer Michael C. Nolan. "Double, or binary, asteroid systems are known to be fairly common — about one in six near-Earth asteroids is a binary — but this is the first near-Earth triple system to be discovered."
Most asteroids orbit the sun between Mars and Jupiter. But some are closer in. One recently missed Mars by a cosmic smidgeon.
Near-Earth asteroids are of particular interest because of the possibility they might cross our path some day, as has happened many times in the past. One flew past Earth just last month, in fact. However, 2001 SN263 is not on a collision course with our planet.
Yet asteroids hold many mysteries for astronomers. Nolan said this finding prompts several questions: Are the objects orbiting in the same plane? How rapidly are the orbits changing with time? Did the smaller objects, which Nolan calls moons, form when this asteroid system formed in the main asteroid belt, or after it arrived in near-Earth space?
"Examining the orbits of the moons as we continue to observe 2001 SN263 over the next few weeks may allow us to determine the density of the asteroid and type of material from which it is made," he said. "We will also be studying its shape, surface features and regolith [blanketing material] properties."
The new observations were made Feb. 11 and the discovery announced Wednesday evening. Arecibo is operated for the National Science Foundation by Cornell's National Astronomy and Ionosphere Center.
Triple Asteroid Found Near Earth
Mars Express Yields Provocative Observations
Europe's Mars Express is gathering data regarding the geological and atmospheric processes on the red planet -- information that might shore up the case that present-day life is percolating subsurface.
Recent analyses of data gleaned by the Planetary Fourier Spectrometer (PFS) carried by the spacecraft reveal that concentrations of water vapor and methane in the atmosphere of Mars significantly overlap.
New in-depth looks at the PFS data also bears out that methane is not uniform in the atmosphere, but thick in some areas. The PFS team observed that the areas of highest concentration of methane overlap with the areas where water vapor and underground water ice are also concentrated.
This spatial correlation between water vapor and methane seems to point to a common underground source.
One exciting prospect bolstered by the data: Can forms of bacterial life exist in the water below the ice table, producing methane and other gases and releasing them to the surface and then to the atmosphere? Indeed, the PFS data could be hinting at the presence of extant life on Mars in terms of the presence of 'biomarker' gases.
Concentrated in regions
The Mars Express data and what they could mean were reported today by Vittorio Formisano, PFS principal investigator, at the International Mars Conference being held this week in Ischia, Italy, and organized by the Italian Space Agency.
The PFS is an Italian Space Agency instrument, developed by the Istituto di Fisica dello Spazio Interplanetario (IFSI) of the Istituto Nazionale di Astrofisica (INAF).
ESA released today an overview of the PFS data, noting that at 6-9 miles (10-15 kilometers) above the surface, water vapor is well mixed and uniform in the atmosphere. However, the instrument found that, close to the surface, water vapor is more concentrated in three broad equatorial regions: Arabia Terra, Elysium Planum and Arcadia-Memnonia.
In those locales on Mars, the concentration is two to three times higher than in other regions observed. These particular areas of water vapor concentration also match up with places that NASA's Mars Odyssey spacecraft found a water ice layer just below the Martian surface, Formisano reported.
Ice table
The ESA press statement also explained that an underground ice layer - dubbed an "ice table" - could be the product of geothermal heat from below the surface that pushes water and other material towards the surface. It would then freeze before getting there, due to the very low surface temperature on Mars.
While further investigations are needed to fully understand the correlation between the ice table and the presence and distribution of water vapor and methane in the atmosphere, the ESA statement today poses several questions:
Can the geothermal processes which 'feed' the ice table also push water vapor and other gases, like methane, to the surface?
Can there be liquid water below the ice table?
Can forms of bacterial life exist in the water below the ice table, producing methane and other gases and releasing them to the surface and then to the atmosphere?
Provocative observations
"This is great news," said James Garvin, Chief Scientist for Mars and the Moon and Deputy Exploration Chief Scientist within the Science Mission Directorate at NASA Headquarters, Washington, D.C.
"All of us are encouraged by this first 'retrieval' from Mars orbit of such noteworthy species [gases], clearly relevant to the photochemical evolution of Mars and potentially linked to provocative possibilities, including active volcanism among others."
Garvin added that "the real test" will come when the broadest possible participation by the international community gains an opportunity to analyze these new data, given the potentially controversial nature. "That's the way science breakthroughs gain standing in the science community."
While "encouraged, excited, and delighted" that the Mars Express PFS investigators have reported such provocative observations, Garvin said the findings must undergo open peer
review by external experts, including those who have made similar detections from Earth-based systems.
Corroboration needed
Garvin explained that NASA's Mars Odyssey detected a higher concentration of hydrogen, not necessarily water ice. Mars Odyssey cannot observe "water ice layers", Garvin said, only the presence of hydrogen.
Furthermore, that hydrogen, he added, could be due to hydrated minerals, such as those found on the surface by the Mars Exploration Rovers and also detected from orbit by the Mars Express OMEGA imaging spectrometer.
In Garvin's view, the real test will come when future spectrometers -- such as those destined to fly aboard the NASA Phoenix lander to be launched in 2007, and potentially carried on the Mars Science Laboratory in 2009 -- corroborate the Mars Express measurements.
Red Planet Radar: Probing the Martian Underground for Water
European researchers hope to pin down exactly where Mars is hiding its water by looking through the planet rather than on its surface.
A ground penetrating radar system aboard Mars Express, a European Space Agency (ESA) probe set to launch in early June, will use radio waves to map out any water reservoirs as deep as 3 miles (5 kilometers) below the surface.
"We are looking for serious amounts of water, for mountains of the stuff," said Iwan Williams, a professor with Queen Mary University of London and co-investigator of the radar experiment. "Everybody believes that it's there."
Williams told SPACE.com he hopes the radar aboard Mars Express will provide definitive answers as to where to find subsurface water, the existence of which has, to date, only been inferred through satellite observations.
Radioing in on Mars' insides
The Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument, called MARSIS, is one of seven riding aboard the Mars Express probe along with the Beagle 2 lander that will search for evidence of water and life on the planet's surface.
Once in orbit, the 131-foot (40-meter) MARSIS antenna boom will unfurl from Mars Express, a craft with a widest point of 6 feet (1.8 meters). "The antenna folds up like a magician's trick," Williams said. "You just push a button and away it goes."
MARSIS will simultaneously send out low frequency radio waves at two different frequencies to make its radar soundings. Although the majority of these of signals are reflected by the Martian surface, some will make it deep enough to relay information about the planet's interior composition.
A cache of underground water, for example, should reflect signals more strongly than the surrounding rock, and clue researchers in on its location and size. Weaker radar echoes should allow MARSIS to determine the thickness of sand dunes and examine the different layers of Martian rock underground.
"Water is really what you want to see," said Gerhard Schewm, head of the Planetary Missions Division at ESA, in a telephone interview. "And not just water in mineral deposits, but liquid water."
Because the radio frequencies are so low -- between 1.3 and 5.5 megahertz -- researchers plan to make the most of their subsurface observations at night to prevent interference by the Martian atmosphere during the day, when free electrons in Mars' ionosphere will reflect much of MARSIS' radar signals. Researchers also have to wait until Mars Express is within 500 miles (800 kilometers) of the planet to take accurate radar soundings, giving researchers about 26 minutes during each 6.75-hour orbit to look for underground water.
But instead of sitting idly by during the Martian day, MARSIS will bounce signals off the planet's ionosphere to measure the effect of solar wind in the upper atmosphere and attempt to make subsurface observations when possible, researchers said.
The MARSIS experiment is the result of collaboration between ESA and NASA's Jet Propulsion Laboratory in Pasadena, California.
Watery Mars
Once thought to be a dry, arid planet covered in red dirt, Mars now seems to be no stranger to water. Two NASA probes, Mars Odyssey and Mars Global Surveyor, have recorded data that point toward the existence of water on the Red Planet.
Earlier this year, researchers poring over data from Mars Global Surveyor announced that the planet's ice caps consisted mostly of water, not frozen carbon dioxide as had been previously thought for decades. Global maps generated by Mars Odyssey as it orbited the planet found large amounts of subsurface hydrogen thought to exist as water or ice, so much so that it could cover the planet in ankle-deep water.
"If [water] is not there, it has serious implications for the study of Mars," Williams said, adding that water has always been a cornerstone for many scientists exploring the possibility of life on Mars and eventual human exploration there. "Without it, the planet becomes a much more inhospitable place."
MARSIS should be able to observe most of Mars over the course of one Martian Year, about 687 Earth days, and allow researchers to build up a three-dimensional representation of the planet's upper crust.
"This is a very important instrument," Schwehm said of MARSIS. "It will give us a global view of the Mars subsurface and allow us to see the structure of water distribution there."
The findings from MARSIS, he added, will add to those of the Beagle 2 lander, the orbiting Mars Odyssey and Global surveyor, as well as the upcoming robotic rovers NASA expects to launch in June.
