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Wednesday, 18 February 2009

Distant planets and Spirit's new moods

Today:

  1. Astronomers get a sizzling weather report from a distant planet
  2. Mars Rover Team Diagnosing Unexpected Behavior
  3. Cassini Finds Hydrocarbon Rains May Fill Titan Lakes
  4. Apollo 17 sample helps date Moon

Astronomers get a sizzling weather report from a distant planet

January 28th, 2009

Astronomers have observed the intense heating of a distant planet as it swung close to its parent star, providing important clues to the atmospheric properties of the planet. The observations enabled astronomers at the University of California, Santa Cruz, to generate realistic images of the planet by feeding the data into computer simulations of the planet's atmosphere.

The researchers used NASA's Spitzer Space Telescope to obtain infrared measurements of the heat emanating from the planet as it whipped behind and close to its star. In just six hours, the planet's temperature rose from 800 to 1,500 Kelvin (980 to 2,240 degrees Fahrenheit).

Known as HD 80606b, the planet circles a star 200 light years from Earth, is four times the mass of Jupiter, and has the most eccentric orbit of any known planet. It spends most of its 111.4-day orbit at distances that would place it between Venus and Earth in our own solar system, while the closest part of its orbit brings it within 0.03 astronomical units of its star (one astronomical unit is the distance between Earth and the Sun). The planet zips through this dramatic close encounter with its star in less than a day.

Spitzer observed the planet for 30 hours before, during, and just after its closest approach to the star. The planet passed behind the star (an event called a secondary eclipse) just before the moment of its closest approach. This was a lucky break for Laughlin and his colleagues, who had not known that would happen when they planned the observation. The secondary eclipse allowed them to get accurate measurements from just the star and thereby determine exact temperatures for the planet.

The extreme temperature swing observed by Spitzer indicates that the intense irradiation from the star is absorbed in a layer of the planet's upper atmosphere that absorbs and loses heat rapidly, Laughlin said.

Coauthor Jonathan Langton, a postdoctoral researcher at UCSC, fed the Spitzer data into a hydrodynamic model of the planet's atmosphere to predict its response to the intense heating. Langton's simulation shows the global storms and shockwaves unleashed in the planet's atmosphere every 111 days as it swings close to its star.

"The initial response could be described as an explosion on the side facing the star," Langton said. "As the atmosphere heats up and expands, it produces very high winds, on the order of 5 kilometers per second, flowing away from the day side toward the night side. The rotation of the planet causes these winds to curl up into large-scale storm systems that gradually die down as the planet cools over the course of its orbit."

Daniel Kasen was able to generate photorealistic images of the planet using a program he developed to calculate radiative transfer processes in astrophysics. "

The resulting images show a thin blue crescent of reflected starlight framing the night side of the planet, which glows cherry red from its own heat, like coals in a fire. "These images are far more realistic than anything that's been done before for extrasolar planets," Laughlin said. source

My comment: I find it absolutely cool how we can know what's happening on a planet 200 l.y. away from our own! We can get a pretty good idea what it looks like, or what happens when it passes near its star. Also interesting is that the heat is absorbed by the upper atmosphere. Imagine what could go on inside the giant. I mean, we know so little about our own Jupiter!

Mars Rover Team Diagnosing Unexpected Behavior

January 28th, 2009
(PhysOrg.com) -- The team operating NASA's Mars Exploration Rover Spirit plans diagnostic tests this week after Spirit did not report some of its weekend activities, including a request to determine its orientation after an incomplete drive.

On Sunday, during the 1,800th Martian day, or sol, of what was initially planned as a 90-sol mission on Mars, information radioed from Spirit indicated the rover had received its driving commands for the day but had not moved. That can happen for many reasons, including the rover properly sensing that it is not ready to drive. However, other behavior on Sol 1800 was even more unusual: Spirit apparently did not record the day's main activities into the non-volatile memory, the part of its memory that persists even when power is off.

On Monday, Spirit's controllers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., chose to command the rover on Tuesday, Sol 1802, to find the sun with its camera in order to precisely determine its orientation. Not knowing its orientation could have been one possible explanation for Spirit not doing its weekend drive. Early Tuesday, Spirit reported that it had tried to follow the commands, but had not located the sun.

"We don't have a good explanation yet for the way Spirit has been acting for the past few days," said JPL's Sharon Laubach, chief of the team that writes and checks commands for the rovers.

Despite the rover's unexplained behavior, Mars Exploration Rovers' Project Manager John Callas of JPL said Wednesday, “Right now, Spirit is under normal sequence control, reporting good health and responsive to commands from the ground." source

My comment: Ok, first, why did they call the Martian day "sol". It's kind of weird. Anyway, that's not even part of the weirdness. So, dear old Spirit, decided that it's having a time off work? As funny as it sounds, its behaviour is very odd. Sure, it could have problems moving or locating the Sun, but not recording them is very odd. I wonder what happened with the poor guy. It's very suspicious. I guess it either was used for a party of the little (or not so little) green guys or it developed AI. a link to the story suggesting everything is fine now.

Cassini Finds Hydrocarbon Rains May Fill Titan Lakes

January 30th, 2009

(PhysOrg.com) -- A region on Saturn's moon Titan's southern latitudes appears to have been flooded by a summer cloudburst of hydrocarbon rain, as seen in images from NASA's Cassini spacecraft taken before and after a large storm system was observed.

Recent images of Titan from NASA’s Cassini spacecraft affirm the presence of lakes of liquid hydrocarbons by capturing changes in the lakes brought on by rainfall.

For several years, Cassini scientists have suspected that dark areas near the north and south poles of Saturn’s largest satellite might be liquid-filled lakes. An analysis published today in the journal Geophysical Research Letters of recent pictures of Titan's south polar region reveals new lake features not seen in images of the same region taken a year earlier. The presence of extensive cloud systems covering the area in the intervening year suggests that the new lakes could be the result of a large rainstorm and that some lakes may thus owe their presence, size and distribution across Titan’s surface to the moon’s weather and changing seasons.

The high-resolution cameras of Cassini’s Imaging Science Subsystem (ISS) have now surveyed nearly all of Titan’s surface at a global scale.

Such observations have documented greater stores of liquid methane in the northern hemisphere than in the southern hemisphere. And, as the northern hemisphere moves toward summer, Cassini scientists predict large convective cloud systems will form there and precipitation greater than that inferred in the south could further fill the northern lakes with hydrocarbons.

Some of the north polar lakes are large. If full, Kraken Mare is 400,000 square kilometers. All the north polar dark ‘lake’ areas observed by ISS total more than 510,000 square kilometers -- almost 40 percent larger than Earth’s largest “lake,” the Caspian Sea.

However, evaporation from these large surface reservoirs is not great enough to replenish the methane lost from the atmosphere by rainfall and by the formation and eventual deposition on the surface of methane-derived haze particles.

Combined with previous analyses, the new observations suggest that underground methane reservoirs must exist.

Titan is the only satellite in the solar system with a thick atmosphere in which a complex organic chemistry occurs. "It’s unique," Turtle said. source

My comment: Oh, well, enough is said in the article. I'd just like to remind you that Titan is one of the Top candidates in our Solar System to host life.


Apollo 17 sample helps date Moon

A SPECK of the mineral zircon that's older than any yet found on Earth has been recovered from a rock sample brought back by Apollo 17 astronauts. The grain has helped pinpoint the age at which the molten moon solidified.

Until now, the zircon found in lunar rocks was between 3.90 and 4.35 billion years old, the same as the oldest zircon found on Earth. But many of these lunar grains came from low-lying areas on the moon, where the crust had been resurfaced after being melted by meteorite impacts.

The new sample, found by Alexander Nemchin at Curtin University of Technology in Perth, Australia, and colleagues, is 4.42 billion years old, and came from the lunar highlands. That means it crystallised after the crust first solidified, within 100 million years of the moon's formation .

The grain sets limits on the moon's age, says Dianne Taylor of the University of California, Los Angeles, who has studied similar samples. The moon is thought to have formed from debris ejected by a giant impact between Earth and a smaller body between 10 and 100 million years after the formation of the solar system, 4.57 billion years ago. Taylor reckons the lunar crust formed within 90 million years of the impact, which tallies well with the age of the zircon. source

My comment: I don't know what exactly that means, except that it probably makes the Earth even older if we keep the theory that the Moon is part of the Earth.

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