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Thursday, 9 April 2009

Planets special, 03.2009

Today:

  1. NASA Spacecraft Falling For Mars
  2. NASA and ESA prioritize outer planet
  3. The lower atmosphere of Pluto revealed
  4. Gullies on Mars show tantalizing signs of recent water activity
  5. Mountain on Mars may answer big question
If you're a sci fi fan, you simply cannot stay unimpressed by the following news. It would be so cool to be able to visit all the places in the Solar System (though, it's pretty big if you think about it, we can't even visit the all of the places on Earth) and explore them and discover their secrets. Oh, well, maybe next decade :)

NASA Spacecraft Falling For Mars

February 13th, 2009

(PhysOrg.com) -- Launched in September of 2007, and propelled by any one of a trio of hyper-efficient ion engines, NASA's Dawn spacecraft passed the orbit of Mars last summer. At that time, the asteroid belt (where Dawn's two targets, asteroid Vesta and the dwarf planet Ceres reside), had never been closer. In early July the spacecraft began to lose altitude, falling back towards the inner solar system. Then on October 31, 2008, after 270 days of almost continuous thrusting, the ion drive turned off.

A gravity assist is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save fuel, time and expense. A spacecraft traveling to an outer planet (or in this case asteroid) will decelerate because the incessant tug of the sun's gravity slows it down. By flying a spacecraft close by a large planet and its large gravity field, some of the planet's speed as it orbits the sun is transferred to the spacecraft. In Dawn's case, it is using the Red Planet's tremendous angular momentum (the speed at which Mars orbits the sun) to give it a little extra oomph.

"A big oomph actually," said Rayman. "The gravity of Mars will change Dawn's path about the sun, enlarging its elliptical orbit and sending the probe farther from the sun. It will also change Dawn's orbital plane by more than 5 degrees. This is important because Dawn has to maneuver into the same plane in which Vesta orbits the sun."

If Dawn had to perform these orbital adjustments on its own with no Mars gravitational deflection, it would have required the spacecraft to fire up its engines and change velocity by more than 5,800 miles per hour (9,330 kilometers per second). Such velocity changes would have required Dawn to carry an extra 230 pounds (104 kilograms) of xenon fuel.

But the Mars gravity assist is not the final hurdle on Dawn's road to the asteroid belt. The subsequent 30 months include more than 27 months of blue-green tinged ion thrusting to successfully rendezvous with Dawn's first target -Vesta.

Dawn's 4.8-billion-kilometer (3-billion-mile) odyssey includes orbiting asteroid Vesta in 2011 and the dwarf planet Ceres in 2015. These two giants of the asteroid belt have been witness to much of our solar system's history. By using Dawn's instruments to study both objects for several months, scientists can more accurately compare and contrast the two. Dawn's science instrument suite will measure geology, elemental and mineral composition, shape, surface topography, geomorphology and tectonic history, and will also seek water-bearing minerals. In addition, the Dawn spacecraft's orbit characteristics around Vesta and Ceres will be used to measure the celestial bodies' masses and gravity fields. source

My comment: Lovely! One can only be amazed how we, on Earth, manage to drive a mission around Mars and away to the outer edge of the Solar system. I know we can do it, but still, it's great to see it in action. Enjoy!

NASA and ESA prioritize outer planet missions

February 18th, 2009

At a meeting in Washington last week, NASA and ESA officials decided to first pursue a mission to study Jupiter and its four largest moons, and plan for another mission to visit Saturn's largest moon, Titan, and Enceladus.

The proposed projects are grand endeavours that set the stage for future planetary science research. These outer-planet flagship missions could eventually answer questions about how our Solar System formed and whether habitable conditions exist elsewhere in the Solar System.

The missions, called the Europa Jupiter System Mission and the Titan Saturn System Mission, are the result of the merger of separate NASA and ESA mission concepts. Based on studies and stringent independent assessment reviews, the US Europa Jupiter System Mission, called Laplace in Europe, was the technically more feasible to implement first. However, ESA's Solar System Working Group concluded that the scientific merits of both missions could not be separated. The group declared, and NASA agreed, that both missions should move forward for further study and implementation.

"The decision means a win, win situation for all parties involved," said Ed Weiler, associate administrator for NASA's Science Mission Directorate in Washington. "Although the Jupiter system mission has been chosen to proceed to an earlier flight opportunity, a Saturn system mission clearly remains a high priority for the science community."

Both agencies will need to undertake several more steps and detailed studies before officially moving forward.

The Europa Jupiter System Mission will use two robotic orbiters to conduct unprecedented detailed studies of the giant gaseous planet Jupiter and its moons Io, Europa, Ganymede and Callisto. NASA will build one spacecraft, initially named Jupiter Europa Orbiter. ESA will build the other spacecraft, initially named Jupiter Ganymede Orbiter. The two spacecraft are scheduled to launch in 2020 on two separate launch vehicles from different launch sites. They will reach the Jupiter system in 2026 and spend at least three years conducting research.

Europa, with its putative ocean, is a unique target to study habitability around the gas giant. Ganymede, the largest moon in the Solar System, is the only moon known to have its own internally-generated magnetic field and is also suspected to have a deep undersurface water ocean. Scientists long have sought to understand the causes of the magnetic field. Io, the most volcanically active body in the Solar System, and Callisto, whose surface is heavily cratered and ancient, providing a record of events from the early history of the Solar System, are also key targets of the Jupiter System Mission.

The Titan Saturn System Mission would consist of a NASA orbiter and an ESA lander and research balloon. The complex mission poses several technical challenges requiring significant study and technology development. NASA will continue to study and develop those technologies.

ESA's Directorate of Science and Robotic Exploration will manage the European contribution to the Jupiter mission. NASA's Jet Propulsion Laboratory in Pasadena, California, will manage NASA's contributions to the projects for NASA's Science Mission Directorate in Washington. source

My comment: Well, it was more logical for Europe to lead the missions to Europa, but maybe now, there's more symmetry. In any case, I'm glad they choose to proceed with both of the missions, because they are so important! Can't wait to see them in action.

The lower atmosphere of Pluto revealed

March 2nd, 2009

(PhysOrg.com) -- "With lots of methane in the atmosphere, it becomes clear why Pluto's atmosphere is so warm," says Emmanuel Lellouch, lead author of the paper reporting the results.

Pluto, which is about a fifth the size of Earth, is composed primarily of rock and ice. As it is about 40 times further from the Sun than the Earth on average, it is a very cold world with a surface temperature of about minus 220 degrees Celsius!

It has been known since the 1980s that Pluto also has a tenuous atmosphere, which consists of a thin envelope of mostly nitrogen, with traces of methane and probably carbon monoxide. As Pluto moves away from the Sun, during its 248 year-long orbit, its atmosphere gradually freezes and falls to the ground. In periods when it is closer to the Sun — as it is now — the temperature of Pluto's solid surface increases, causing the ice to sublimate into gas.

Until recently, only the upper parts of the atmosphere of Pluto could be studied. By observing stellar occultations, a phenomenon that occurs when a Solar System body blocks the light from a background star, astronomers were able to demonstrate that Pluto's upper atmosphere was some 50 degrees warmer than the surface, or minus 170 degrees Celsius. These observations couldn't shed any light on the atmospheric temperature and pressure near Pluto's surface. But unique, new observations made with the CRyogenic InfraRed Echelle Spectrograph (CRIRES), attached to ESO's Very Large Telescope, have now revealed that the atmosphere as a whole, not just the upper atmosphere, has a mean temperature of minus 180 degrees Celsius, and so it is indeed "much hotter" than the surface.

In contrast to the Earth's atmosphere, most, if not all, of Pluto's atmosphere is thus undergoing a temperature inversion: the temperature is higher, the higher in the atmosphere you look. The change is about 3 to 15 degrees per kilometre. On Earth, under normal circumstances, the temperature decreases through the atmosphere by about 6 degrees per kilometre.

The reason why Pluto's surface is so cold is linked to the existence of Pluto's atmosphere, and is due to the sublimation of the surface ice; much like sweat cools the body as it evaporates from the surface of the skin, this sublimation has a cooling effect on the surface of Pluto. In this respect, Pluto shares some properties with comets, whose coma and tails arise from sublimating ice as they approach the Sun.

The CRIRES observations also indicate that methane is the second most common gas in Pluto's atmosphere, representing half a percent of the molecules. "We were able to show that these quantities of methane play a crucial role in the heating processes in the atmosphere and can explain the elevated atmospheric temperature," says Lellouch.

Two different models can explain the properties of Pluto's atmosphere. In the first, the astronomers assume that Pluto's surface is covered with a thin layer of methane, which will inhibit the sublimation of the nitrogen frost. The second scenario invokes the existence of pure methane patches on the surface. source

My comment: Another fascinating story. If you only consider how far Pluto is from Earth, it's absolutely cool that we're able to measure the gradient in its atmosphere. At least I'm awed, even though I'm an astrophysicist. People do so much cool stuff lately, it's hard to keep up with everything that's going on.

Gullies on Mars show tantalizing signs of recent water activity

(PhysOrg.com) -- Planetary geologists at Brown University have found a gully fan system on Mars that formed about 1.25 million years ago. The fan offers compelling evidence that it was formed by melt water that originated in nearby snow and ice deposits and may stand as the most recent period when water flowed on the planet.

Gullies are known to be young surface features on Mars. But scientists studying the planet have struggled with locating gullies they can conclusively date. In a paper that appears on the cover of the March issue of Geology, the Brown geologists were able to date the gully system and hypothesize what water was doing there.

The gully system shows four intervals where water-borne sediments were carried down the steep slopes of nearby alcoves and deposited in alluvial fans, said Samuel Schon, a Brown graduate student and the paper's lead author.

The finding comes on the heels of discoveries of water-bearing minerals such as opals and carbonates, the latter of which was announced by Brown graduate student Bethany Ehlmann in a paper in Science in December. Those discoveries build on evidence that Mars was occasionally wet far longer than many had believed, and that the planet may have hosted a warm, wet environment in some places during its long history.

However, the finding of a gully system, even an isolated one, that supported running water as recently as 1.25 million years ago greatly extends the time that water may have been active on Mars. It also adds to evidence of a recent ice age on the planet when polar ice is believed to have been transported towards the equator and settled in mid-latitude deposits, said James Head III, professor of geological sciences at Brown, who first approximated the span of the martian ice age in a Nature paper in 2003.

"We think there was recent water on Mars," said Head, who with Brown postdoctoral researcher Caleb Fassett is a contributing author on the paper. "This is a big step in the direction to proving that."

The gully system is located on the inside of a crater in Promethei Terra, an area of cratered highlands in the southern mid-latitudes. The eastern and western channels of the gully each run less than a kilometer from their alcove sources to the fan deposit.

The team determined that ice and snow deposits formed in the alcoves at a time when Mars had a high obliquity (its most recent ice age) and ice was accumulating in the mid-latitude regions. Sometime around a half-million years ago, the planet's obliquity changed, and the ice in the mid-latitudes began to melt or, in most instances, changed directly to vapor. Mars has been in a low-obliquity cycle ever since, which explains why no exposed ice has been found beyond the poles. source

My comment: Another "Cool!". What more can I say.

Mountain on Mars may answer big question

March 4th, 2009

The Martian volcano Olympus Mons is about three times the height of Mount Everest, but it's the small details that Rice University professors Patrick McGovern and Julia Morgan are looking at in thinking about whether the Red Planet ever had - or still supports - life.

Using a computer modeling system to figure out how Olympus Mons came to be, McGovern and Morgan reached the surprising conclusion that pockets of ancient water may still be trapped under the mountain. Their research is published in February's issue of the journal Geology.

The scientists explained that their finding is more implication than revelation. "What we were analyzing was the structure of Olympus Mons, why it's shaped the way it is," said McGovern.

In modeling the formation of Olympus Mons with an algorithm known as particle dynamics simulation, McGovern and Morgan determined that only the presence of ancient clay sediments could account for the volcano's asymmetric shape. The presence of sediment indicates water was or is involved.

Olympus Mons is tall, standing almost 15 miles high, and slopes gently from the foothills to the caldera, a distance of more than 150 miles. That shallow slope is a clue to what lies beneath, said the researchers. They suspect if they were able to stand on the northwest side of Olympus Mons and start digging, they'd eventually find clay sediment deposited there billions of years ago, before the mountain was even a molehill.

The European Space Agency's Mars Express spacecraft has in recent years found abundant evidence of clay on Mars. This supports a previous theory that where Olympus Mons now stands, a layer of sediment once rested that may have been hundreds of meters thick.

Morgan and McGovern show in their computer models that volcanic material was able to spread to Olympus-sized proportions because of the clay's friction-reducing effect, a phenomenon also seen at volcanoes in Hawaii.

What may be trapped underneath is of great interest, said the researchers. Fluids embedded in an impermeable, pressurized layer of clay sediment would allow the kind of slipping motion that would account for Olympus Mons' spread-out northeast flank - and they may still be there.

Thanks to NASA's Phoenix lander, which scratched through the surface to find ice underneath the red dust last year, scientists now know there's water on Mars. So Morgan and McGovern feel it's reasonable to suspect water may be trapped in pores in the sediment underneath the mountain. source

My comment:That's why I so love modelling. Because it lets you peak into the kitchen of the Universe. Now all we need is a thermal and seismic picture of the planet. Can you even imagine that under that volcano may be there's a layer of mud?! Maybe even full of bacterias! Maybe even underground cities :P Ok, it's late here, I'm off to bed. But today's post will definitely make my dreams go sci fi!

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