March 2004 astro bytes
Mars methane, why asteroids head Earthward, rover wrap up, and more
March 1, 2004
March 30, 2004
Mars Express, which went into orbit around the Red Planet on December 25, 2003, has detected methane in the martian atmosphere.
Photo by European Space Agency
Mars Express confirms martian methane
With the two NASA rovers receiving so much attention due to their amazing photography and historic discoveries, sometimes the ESA's martian orbiter is forgotten. Mars Express, however, has made an important find concerning the Red Planet.
Recent observations by Mars Express have revealed methane in Mars's atmosphere. The Planetary Fourier Spectrometer (PFS) aboard the orbiter detected the substance's presence by examining how the molecules interact with sunlight they absorb.
While methane was found, it was measured in small amounts — approximately ten parts in one thousand million. Even this small amount, though, confirms its existence, raising the question, "Where does the methane come from?" However, scientists must understand more about its presence before targeting its origin.
"Since the methane presence is so small, we need to take more measurements," explains Vittorio Formisano, principal investigator for the PFS instrument. "Only then will we have enough data to make a statistical analysis and understand whether there are regions of the atmosphere where methane is more concentrated."
Once they understand more about the substance's distribution and concentration, scientists will attempt to develop a connection between the planet-wide dissemination of methane and potential atmospheric or surface sources that may produce it.
— Jeremy McGovern
Going my way?
A gentle nudge from solar heating sends asteroids toward Earth. A study of asteroids by Paolo Paolicchi (University of Pisa, Italy) and three other astronomers confirms that the Yarkovsky effect has the power to feed main-belt asteroids into Earth-approaching paths. The Yarkovsky effect is a tiny thrust generated by heat radiated from the afternoon side of an asteroid, which is warmer than its morning side. If the asteroid rotates in the same direction as Earth (prograde), then the Yarkovsky thrust minutely accelerates the asteroid, enlarging its orbit. The inverse happens in cases of retrograde rotation.
Writing in the March 25, 2004, issue of Nature, the astronomers describe a study of 21 asteroids that have moved out of the main belt and into Earth-approaching orbits. Of these, 14 show retrograde spins, the rest being prograde. The astronomers concluded that the numbers should be about evenly matched if asteroids in the main belt had entered Earth-crossing orbits through collisions, the method previously suspected of generating Earth-crossers. But the numbers aren't equal.
Retrograde spins are prevalent among Earth-approaching asteroids, say the astronomers, because these see their orbits shrink due to the Yarkovsky effect. Such asteroids slowly drift sunward within the main belt — until they reach a major gravitational lockstep with Jupiter. One such place is the so-called 3:1 resonance, located in the middle of the main belt at 2.5 times the Earth-Sun distance. Asteroids at that location circle the Sun three times each jovian year and find their orbits altered by the big planet's powerful gravity. This sends them out of the main belt and into orbits that cross Earth's.
— Robert Burnham
|March 26, 2004|
Rover wrap up
The Mars rover Spirit has nearly ended its survey of the ejecta-strewn rim of Bonneville Crater. Mission scientists are drilling an 8-millimeter-deep RAT (rock abrasion tool) hole in a basaltic rock nicknamed Mazatzal. This is a block of ejecta on Bonneville's rim that's well embedded in the ground. It has a fluted upper surface deeply sculpted by wind-blown dust and sand. Scientists are drilling the hole to see if the rock changes character with depth.
After finishing at Bonneville, Spirit will drive southeast toward the Columbia Hills, which lie about 1.3 miles (2.3 kilometers) away. Scientists think the hills contain older rocks not yet encountered on the plains because more recent lava flows have buried them. The journey to the hills is expected to take between 60 and 90 sols (Mars days). On the way, the rover will survey the ground it crosses and stop as often as scientists wish to examine targets of interest.
Half the planet away in Meridiani Planum, the other rover, Opportunity, has driven out of Eagle Crater, where it landed and spent the next 57 sols. Scientists have established that the bottom of this crater contains basaltic rock that transitions into the hematite-rich layer at the surface. The hematite is concentrated in "blueberries," spherules between 1 and 3 mm across whose origin is unclear.
The mission plan for Opportunity calls for it to drive east-southeast toward Endurance Crater. There, scientists hope to examine a larger exposure of the sulfate-rich layer that formed an outcrop inside Eagle Crater. This layer was deposited at a time when the landing site was underwater, near the shore of an acidic sea.
In other developments, mission controllers plan to start shifting work schedules away from a Mars-centric time frame, in which each rover's crew works during martian daytime for its assigned rover. The crews will return to using a normal Earth-based schedule. This is expected to make life a lot easier for the crews; the change is partly a result of the mission going smoothly. — Robert Burnham
MESSENGER's launch date postponed
The launch of MESSENGER, NASA's Mercury-orbiting spacecraft, has shifted from May 11, 2004, to sometime within a 15-day window running July 30 through August 13, 2004. The change was made to give engineers more time to test MESSENGER's fault-protection software and also to prepare the spacecraft for launch under less schedule pressure.
The new mission flight plan calls for launch, followed by a flyby of Earth on July 29, 2005, for a course correction. Next come two Venus encounters, on October 23, 2006, and June 4, 2007. The spacecraft then flies past Mercury three times (on January 14, 2008; October 6, 2008; and September 29, 2009) before firing its engine to enter Mercury orbit on March 18, 2011. Once MESSENGER has reached orbit around Mercury, the nominal mission will last one Earth year.
The three Mercury flybys, which all zoom by the planet at an altitude of about 120 miles (200 kilometers), will give scientists a chance to fill in some gaping holes in their data. These include photographing the still-unseen half of Mercury that was not imaged by Mariner 10 in 1974-75. (Mariner 10 is the only spacecraft to have visited Mercury so far.)
MESSENGER is an acronym for MErcury Surface, Space ENvironment, GEochemistry, and Ranging. — Robert Burnham
March 12, 2004
The Cassini image reveals dark regions relatively free of high clouds where methane is strongly absorbed, and bright zones where high, thick clouds shield the methane below. Markedly different cloud attributes appear in different latitude bands. The image also shows a high-altitude atmospheric disturbance just south of the equator that has persisted since the 1990s.
Photo by NASA / JPL / Space Science Institute
Cassini views Saturn's methane
On February 16, 2004, the Cassini spacecraft now approaching Saturn took an image of the planet through a near-infrared filter designed to reveal methane gas. In Saturn's atmosphere, methane is uniformly mixed with hydrogen, the main constituent. The image reveals dark regions relatively free of high clouds where methane is strongly absorbed, and bright zones where high, thick clouds shield the methane below. Markedly different cloud attributes appear in different latitude bands. The image also shows a high-altitude atmospheric disturbance just south of the equator that has persisted since the 1990s.
Four of the ringed planet's moons appear in the image as well: Enceladus (310 miles [499 kilometers] across) lies at top right, followed clockwise by Mimas (245 miles [396 km] across), Tethys (659 miles [1,060 km] across), and Rhea (949 miles [1,528 km] across). The imaging team made Mimas and Enceladus appear about three times brighter in the picture than they actually are. Cassini was 41.1 million miles (66.1 million km) from Saturn when the picture was taken. — Francis Reddy
Rosetta to swing past two asteroids
On Thursday, March 11, the Rosetta Science Working Team announced its selection of asteroids that Rosetta will observe during its journey to Comet 67P/Churyumov-Gerasimenko.
The asteroids, named Steins and Lutetia, have rather different properties. Steins is relatively small, with a diameter of a mile or so. Rosetta will fly past Steins on September 5, 2008, during its first excursion into the asteroid belt. It will pass the asteroid at a distance of 1,060 miles (1,700 kilometers) at the relatively low speed of about 5.6 miles (9 km) per second.
Lutetia is a much bigger object, about 62 miles (100 km) across. Rosetta's encounter with this object will take place during its second swing through the asteroid belt. The probe will pass within about 1,860 miles (3,000 km) of Lutetia on July 10, 2010, at a speed of 9.3 miles (15 km) per second.
Rosetta's scientific goals always included the possibility of studying one or more asteroids at close range. However, only after the spacecraft's launch and insertion into interplanetary orbit could mission managers at the European Space Agency assess how much fuel actually was available for such opportunities. Rosetta will not reach its cometary target until 2014. — Francis Reddy
|March 11, 2004|
Next stop, Mercury
MESSENGER, a spacecraft destined to be the first to orbit the planet Mercury, is now in Florida being prepared for launch. MESSENGER — short for the unwieldy name of MErcury Surface, Space ENvironment, GEochemistry, and Ranging — will begin its six-year-long mission with a launch scheduled for May 11.
Mercury remains the least known of the solar system's four innermost planets. MESSENGER, built by the John Hopkins University Applied Physics Laboratory, will start its year-long orbital study of Mercury in July 2009. In the meantime, it will make a trio of Venus flybys in November 2004, August 2005, and October 2006 that will boost the craft toward Mercury. MESSENGER will then make two Mercury flybys — in October 2007 and July 2008 — to fine-tune its path.
You can watch engineers prep MESSENGER via a live webcam here. — Francis Reddy
Water in Leonid meteor trails
A group led by Asta Pellinen-Wannberg of the Swedish Institute for Space Physics in Kiruna, Sweden, reports the spectral signature of water ions in one unusual meteor trail. Most observations of meteors occur at altitudes between 50 and 70 miles (80 and 110 kilometers) because a meteoroid must collide with a large number of atmospheric gas molecules for the trail to become visible. "However, there have been a few observations, hitherto unexplained, of trails at altitudes that are too high for frictional heating and ablation," they write in the February 15, 2004, issue of Geophysical Research Letters.
On November 19, 2002, during the Leonid meteor shower, the Auroral Large Imaging System (ALIS) at Kiruna caught one such trail. The team found two ALIS images of the same trail, each taken using a different filter. At the time, Earth was passing through debris ejected in 1767 from Comet 55P/Tempel-Tuttle, the source of all Leonid meteors.
Their analysis suggests that the meteoroid was a relatively large, icy body and that such objects explain the riddle of visual observations of meteors at unusually high altitudes. "They are relatively rare because the necessary combination of young meteoroid age, size, velocity, and density are not always present," the group concludes, adding that such bodies bring only a negligible amount of water to Earth's atmosphere. — Francis Reddy
March 8, 2004
Spirit drilled into a rock dubbed Humphrey and found bright materials that suggest water once flowed through the rock. Spirit ground into the rock with the abrasion tool located on its robotic arm. Spirit is on its way to a large crater nicknamed Bonneville.
Photo by NASA / JPL
Spirit finds hints of Mars water
NASA announced on Friday that the Mars Exploration Rover named Spirit has found evidence suggesting that water once flowed through volcanic rocks at Gusev Crater. This came hard on the heels of last week's announcement that water once "soaked" rocks at Meridiani Planum, which is being explored by Spirit's twin rover, Opportunity.
When Spirit scraped away the outer layers of a dark volcanic rock nicknamed Humphrey, images revealed cracks and pores lined with bright material. "If we found this rock on Earth, we would say it is a volcanic rock that had a little fluid moving through it," says Ray Arvidson, deputy principal investigator for the rover science instruments.
The amount of water suggested by the possible crystals found in Humphrey is far less than that indicated by Opportunity's findings at Meridiani Planum. Spirit is continuing on its trek toward Bonneville Crater, where it may be able to study deeper rock layers as Opportunity has done. — Francis Reddy
Saturn shows X-rays
This is different from its somehat similar neighbor, Jupiter, where the most intense X-rays are associated with the strong magnetic field near its poles.
Photo by NASA / Univ. of Hamburg / J.Ness et al.
NASA's Chandra X-ray Observatory has made the first observation of X-rays from Saturn. The emissions are collected near the equator instead of polar regions, like on its neighbor Jupiter, which has left astronomers scratching their heads. Another surprise from the gaseous giant is that the distribution of X-ray energy resembles the Sun's.
"This indicates that Saturn's X-ray emission is due to the scattering of solar X-rays by Saturn's atmosphere," says Jan-Uwe Ness of the University of Hamburg. "It's a puzzle, since the intensity of Saturn's X-rays requires that Saturn reflects X-rays fifty times more efficiently than the Moon."
Because they are less capable of spreading X-rays than Saturn, the planetary rings did not show up in the observations.
— Jeremy McGovern
Ground-based telescopes enter the "Dark Ages"
Last month, a team of astronomers using the Keck Observatory in Hawaii and the Hubble Space Telescope announced the discovery of a galaxy so far away that its light was emitted when the universe was just 750 million years old, or 5 percent its current age. The telescopes could see that far back because gravity from an intervening cluster of galaxies created a magnified image of the distant galaxy. "Without the magnification of 25 afforded by the foreground cluster, this early object could simply not have been identified . . . with the present telescopes available," explained Jean-Paul Kneib of the California Institute of Technology, Pasadena, the lead author of the paper detailing the discovery.
Now, a team of French and Swiss astronomers led by Roser Pelló of the Midi-Pyrénées Observatory and including Kneib has reported the first likely spectroscopic confirmation of a galaxy near a redshift of 10. This translates to an age of 460 million years, or 4 percent the current age of the universe. The group used a near-infrared detector on the European Southern Observatory's Very Large Telescope. A massive cluster of galaxies known as Abell 1835 formed the "gravitational lens" responsible for magnifying the distant galaxy, which is designated IR1916.
In a paper to appear in an upcoming issue of Astronomy & Astrophysics, the team notes that under excellent conditions and using strong gravitational lensing, direct observations of galaxies in the "Dark Ages" are possible with ground-based, 8- to 10-meter class telescopes. "We are looking forward to the exploration of this yet unknown territory from the ground and with the forthcoming James Webb Space Telescope," they write.
— Francis Reddy
|March 5, 2004|
So far so good
Launched earlier this week from French Guiana, it appears that the European Space Agency's Rosetta spacecraft is performing up to expectations at this point. Currently orbiting Earth, the spacecraft has begun its ten-year journey to rendezvous with Comet 67P/Churyumov-Gerasimenko. In nearly a year, the orbiter will utilize its first of three gravity assists from Earth to obtain the required energy to reach the comet. Rosetta will utilize a similar maneuver with the Red Planet in 2007, along with Earth in the same year and again in 2009. The goal is for a lander to be released from the orbiter and reach the comet's nucleus. — Jeremy McGovern
March 1, 2004
Can water sources beneath Cerberus Fossae create the torrent required to form Athabasca Valles? Mark Manga says yes, although repeated floods may be neccesary. About 1,000 feet (300m) separates the highest and lowest elevations on this map. Areas shaded blue represent the lowest elevations, while red and brown colors represent higher regions.
Photo by Courtesy of Mark Manga
Floods from Cerberus Fossae
For decades, geologists have been unable to shake themselves of the notion that Mars once held large amounts of water. The presence of martian channels suggests some sort of hydrologic cycle, and their size makes a compelling case that large volumes of water once coursed over the Red Planet's surface.
One area geologists have found particularly interesting is Cerberus Fossae, a linear eruptive fissure north of the martian equator. The fissure appears to be the source of young flow channels within Athabasca Valles. The best explanation to date is that aquifers located deep undergound periodically spilled onto the surface, perhaps flowing along fractures or lava dikes formed during volcanic episodes. A key question is whether a martian aquifer can discharge water fast enough to explain the flood features.
Now, Mark Manga of the University of California, Berkeley has published a model of the floods using existing calculations that estimate subsurface properties on Earth. Manga finds that underground aquifers can indeed explain the Athabasca Valles flood channels. "No unusual physics or properties need to be invoked except perhaps repeated flooding," he writes in the January 15, 2004, issue of the Geophysical Research Letters. — Francis Reddy
|Red Planet peroxide|
Thanks to the close passage of Earth and Mars's orbits in 2003, researchers were able to detect and measure the level of atmospheric hydrogen peroxide on the Red Planet. Although this confirms what scientists have long speculated, it marks the first time they have found a chemical catalyst in a non-Earth atmosphere. These observations were made using the James Clerk Maxwell Telescope atop Mauna Kea, Hawaii.
The key question now is how this finding will influence the search for life on Mars.
"Hydrogen peroxide is actually used as an antiseptic here on Earth, and so it would tend to retard any biological activity on the surface on Mars," explains Todd Clancy of the Space Science Institute in Boulder, Colorado. "For this reason, as well as the ultraviolet radiation, and lack of water, bacteria-like organisms are not expected to be viable on the surface."
With this in mind, Clancy believes the search for martian life should concentrate on subsurface regions. — Jeremy McGovern
Small planet, thick crust
Using Mariner 10 images of Mercury's fault scarps, Francis Nimmo of the University of California, Los Angeles, and T. R. Watters of the Center for Earth and Planetary Studies at the National Air and Space Museum have estimated the depth of the tiny planet's crust.
The scarps probably formed as Mercury's crust cooled and contracted. Their shapes provide clues to the thickness of the brittle layer where the faulting occurred, and this, in turn, hints at Mercury's heat flux at the time. The researchers found that Mercury's heat flux was relatively high and its solid crust comparatively weak. Their study, published in the January 15 issue of Geophysical Research Letters, indicates the crust must be less than 90 miles (140 kilometers) deep - any thicker and it would have melted completely.
Such a depth is about 27 percent of Mercury's total interior volume. In comparison, the ratios for the Moon, Mars, and Venus are roughly 10, 5, and 2 percent, respectively. Earth's crust is unusually thin, occupying just 1 percent of its interior volume. — Francis Reddy
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