The MESSENGER spacecraft will soon run literally on fumes. After more than 10 years traveling in space, nearly four of those orbiting Mercury, the spacecraft has expended most of its propellant and was on course to impact the planet’s surface at the end of March 2015. But engineers on the team have devised a way to use the pressurization gas in the spacecraft’s propulsion system to propel MESSENGER for as long as another month, allowing scientists to collect even more data about the planet closest to the Sun.
“MESSENGER has used nearly all of the onboard liquid propellant. Typically, when this liquid propellant is completely exhausted, a spacecraft can no longer make adjustments to its trajectory. For MESSENGER, this would have meant that we would no longer have been able to delay the inevitable impact with Mercury’s surface,” explained MESSENGER Mission Systems Engineer Dan O’Shaughnessy, of the Johns Hopkins University Applied Physics Laboratory (APL), in Laurel, Md. “However, gaseous helium was used to pressurize MESSENGER’s propellant tanks, and this gas can be exploited to continue to make small adjustments to the trajectory.”
Mercury was long thought to be lacking volatile compounds that cause explosive volcanism. That view started to change when the MESSENGER spacecraft returned pictures of pyroclastic deposits — the telltale signature of volcanic explosions. Now more detailed data from MESSENGER shows that volcanoes exploded on Mercury for a substantial portion of the planet’s history. The findings suggest Mercury not only had volatiles but held on to them for longer than scientists had expected.
The surface of Mercury crackled with volcanic explosions for extended periods of the planet’s history, according to a new analysis led by researchers at Brown University. The findings are surprising considering Mercury wasn’t supposed to have explosive volcanism in the first place, and they could have implications for understanding how Mercury formed.
Mercury was long thought to be bone dry when it comes to volatiles, and without volatiles there can’t be explosive volcanism. But that view started to change in 2008, after NASA’s MESSENGER spacecraft made its first flybys of Mercury. Those glimpses of the surface revealed deposits of pyroclastic ash — the telltale signs of volcanic explosions — peppering the planet’s surface. It was a clue that at some point in its history Mercury’s interior wasn’t as bereft of volatiles as had been assumed.
The International Astronomical Union (IAU) — the arbiter of planetary and satellite nomenclature since its inception in 1919 — recently approved a proposal from the MESSENGER Science Team to assign names to 10 impact craters on Mercury. In keeping with the established naming theme for craters on Mercury, all of the newly designated features are named after “deceased artists, musicians, painters, and authors who have made outstanding or fundamental contributions to their field and have been recognized as art historically significant figures for more than 50 years.”
Ten newly named craters join 114 other craters named since the MESSENGER spacecraft’s first Mercury flyby in January 2008. More information about the names of features on Mercury and the other objects in the Solar System can be found at the U.S. Geological Survey’s planetary nomenclature web site.
Two NASA spacecraft, one studying the Saturn system, the other observing Mercury, are maneuvering into place to take pictures of Earth on July 19 and 20.
The image taken from the Saturn system by NASA’s Cassini spacecraft will occur between 2:27 and 2:42 PDT (5:27 and 5:42 p.m. EDT, or 21:27 and 21:47 UTC) Friday, July 19. Cassini will be nearly 900 million miles (nearly 1.5 billion kilometers) away from Earth. NASA is encouraging the public to look and wave in the direction of Saturn at the time of the portrait and share their pictures via the Internet.
The Cassini Earth portrait is part of a more extensive mosaic — or multi-image picture — of the Saturn system as it is backlit by the sun. The viewing geometry highlights the tiniest of ring particles and will allow scientists to see patterns within Saturn’s dusty rings. Processing of the Earth images is expected to take a few days, and processing of the full Saturn system mosaic will likely take several weeks.
Full Story and Links: http://www.jpl.nasa.gov/news/news.php?release=2013-225
The surface of Mercury is rather different from those of well-known rocky bodies like the Moon and Mars. Early images from the Mariner 10 spacecraft unveiled a planet covered by smooth plains and cratered plains of unclear origin. A team led by Dr. Simone Marchi, a Fellow of the NASA Lunar Science Institute located at the Southwest Research Institute (SwRI) Boulder, Colo., office, collaborating with the MESSENGER team, including Dr. Clark Chapman of the SwRI Planetary Science Directorate, studied the surface to better understand if the plains were formed by volcanic flows or composed of material ejected from the planet’s giant impact basins.
Recent images from NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft provided new insights showing that at least the younger plains resulted from vigorous volcanic activity. Yet scientists were unable to establish limits on how far into the past this volcanic activity may have occurred, or how much of the planet’s surface may have been resurfaced by very old volcanic plains.
“By comparing the measured craters to the number and spatial distribution of large impact basins on Mercury, we found that they started to accumulate at about the same time, suggesting that the resetting of Mercury’s surface was global and likely due to volcanism,” said lead author Dr. Simone Marchi, who has a joint appointment between two of NASA’s Lunar Science Institutes, one at the SwRI in Boulder and another at the Lunar and Planetary Institute in Houston.
By analyzing Mercury’s rocky surface, scientists have been able to partially reconstruct the planet’s history over billions of years. Now, drawing upon the chemical composition of rock features on the planet’s surface, scientists at MIT have proposed that Mercury may have harbored a large, roiling ocean of magma very early in its history, shortly after its formation about 4.5 billion years ago.
The scientists analyzed data gathered by MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging), a NASA probe that has orbited the planet since March 2011. Later that year, a group of scientists analyzed X-ray fluorescence data from the probe, and identified two distinct compositions of rocks on the planet’s surface. The discovery unearthed a planetary puzzle: What geological processes could have given rise to such distinct surface compositions?
To answer that question, the MIT team used the compositional data to recreate the two rock types in the lab, and subjected each synthetic rock to high temperatures and pressures to simulate various geological processes. From their experiments, the scientists came up with only one phenomenon to explain the two compositions: a vast magma ocean that created two different layers of crystals, solidified, then eventually remelted into magma that then erupted onto Mercury’s surface.
New observations by the MESSENGER spacecraft provide compelling support for the long-held hypothesis that Mercury harbors abundant water ice and other frozen volatile materials in its permanently shadowed polar craters.
Three independent lines of evidence support this conclusion: the first measurements of excess hydrogen at Mercury’s north pole with MESSENGER’s Neutron Spectrometer, the first measurements of the reflectance of Mercury’s polar deposits at near-infrared wavelengths with the Mercury Laser Altimeter (MLA), and the first detailed models of the surface and near-surface temperatures of Mercury’s north polar regions that utilize the actual topography of Mercury’s surface measured by the MLA. These findings are presented in three papers published online today in Science Express.
Given its proximity to the Sun, Mercury would seem to be an unlikely place to find ice. But the tilt of Mercury’s rotational axis is almost zero — less than one degree — so there are pockets at the planet’s poles that never see sunlight. Scientists suggested decades ago that there might be water ice and other frozen volatiles trapped at Mercury’s poles.