AstroSpace Update – January 2010
AstroSpace Update
January 2010
Gathered by Don Lynn from NASA and other sources
Cassini (Saturn mission) has observed the strange hexagon at the north pole, since it recently returned to daylight for the 1st time in 15 years, [...]due to the change of seasons on Saturn.
In the dark, Cassini was able to see the hexagon in infrared, but the spacecraft’s visible light instruments have far better resolution. The result revealed concentric circles, curlicues, walls and streamers not seen before. The hexagon was discovered by the Voyager spacecraft nearly 30 years ago, and the figure was found to be largely unchanged since that time. The hexagon is known to be a jet stream blowing around the pole, but why it makes 6 sharp bends has remained unexplained.
Titan lakes – Cassini images of Saturn’s moon Titan show that there are about 20 times as many lakes (of methane) in the northern hemisphere as there are in the southern. There are also more dry lake beds in the north. A new paper explains this as due to Saturn’s eccentric orbit. During Titan’s southern summer, the planet and Titan are closer to the Sun than during the northern summer. This difference increases the methane rainfall in relation to lake evaporation in the north, and hence more lakes form there. Over tens of thousands of years, the perihelion of the orbit moves with respect to the seasons, so eventually the lakes should be more prevalent in the south.
Martian methane was discovered in 1999. Later the rate at which methane is destroyed at Mars was measured, indicating a substantial amount of the gas is being created there every year to replace the loss. 4 sources of the gas have been suggested: volcanic activity releases it, meteorite collision releases it, water acting on certain volcanic rock produces it, or bacteria generate it. The first theory (volcanic) was ruled out a few years ago. A new study rules out the meteorite theory. The new study calculated the rate of methane production that could be a result of meteorites, and it falls far short. The study recreated Martian meteor conditions in the lab and measured methane. That leaves only the 2 most exciting theories: that liquid water or life (or both) exist on Mars. Either would have to be underground.
Spirit (Mars rover) – Mission managers commanded the rover to rotate its wheels several times in an effort to extricate Spirit from the powdery material in which it has been stuck since April. The 1st attempt stopped quickly when the rover exceeded its tip limit, which has been set quite small for safety reasons. The second wheel spin moved the rover more than half an inch, though the wheels spun several feet. That was encouraging, since that is the behavior shown by the other rover when it was stuck in soft material, and repeated spinnings eventually got it out. A later attempt was stopped when Spirit detected that the right rear wheel had stopped turning. Subsequent tests showed that this wheel motor has failed. The right front wheel motor failed 3 years ago, so now only 4 of the 6 wheels can rotate. Then all wheels were tested again, and the wheel broken for the last 3 years turned! So maybe 5 wheels now work. The Free Spirit saga will continue.
Mars Reconnaissance Orbiter (MRO) has been taken out of safe mode and is soon to resume observations. Late in August MRO went into safe mode when the control computer unexpectedly restarted. Subsequent analysis showed that 2 closely spaced safe mode events could be unrecoverable. So MRO was left in safe mode until a fix for this problem could be loaded into its computers, which was accomplished in late November. MRO is also resuming relaying data and commands between Earth and the Mars rovers. During the safe mode, Mars Odyssey (another orbiter) was used to relay the rovers.
Martian rivers – A computer program was written to analyze altitude data regarding Mars in order to identify river valleys by their shape. It found about twice as many as had been identified by eye. The network of valleys supports that the planet in the distant past had frequent rainfall, sparser in the south, which would be explained if a large evaporation source occurred only in the north. Thus the valley network supports also the theory that the northern lowlands were once a sea. Some astronomers had proposed that the river valleys were formed by ground water sapping, not by rainfall, but the abundance of valleys newly found supports rainfall.
Kuiper Belt (icy asteroids beyond Neptune) – The Hubble Space Telescope (HST) has discovered the smallest object ever detected by visible light in the Kuiper Belt. Astronomers analyzing over 4 years of data from the HST guidance sensors found one instance of an object crossing in front of a guide star. Though the object was too dim to be imaged, the drop in light from the star was detectable. The distance was estimated by the time it spent in front of the star (0.3 seconds), and its size (about 3200 feet) was calculated from the amount of dimming. The smallest Kuiper Belt object previously imaged in visible light is about 30 miles across. It has long been predicted that collisions in the Kuiper Belt should produce objects of much smaller sizes than can be detected by normal means, but this discovery is the first observational evidence that such small objects exist. The astronomers plan to analyze the remaining HST guider data to look for more such incidents.
Exoplanets (planets outside our solar system)– A team of planet hunters announced they have discovered 5 and possibly 6 low-mass planets orbiting 2 nearby Sun-like stars. The findings include 2 super-Earths, that is, planets more massive than Earth, but not large enough to be gas giants, so are likely mostly solid rock like our planet. These are the first super-Earths found orbiting Sun-like stars. They have masses of 5 and 7.5 times that of our planet. They are both quite close to their stars, so are too hot to support liquid water or life. Three of the newly discovered planets orbit the star 61 Virginis, a naked-eye star in Virgo, only 28 light-years away. Their masses range from 5 to 25 times that of Earth. The second system found orbits the star HD 1461, a naked-eye star in Cetus, 76 light-years distant. Both systems were discovered using Earth-based telescopes using the radial-velocity method, in which are detected wobbles in a star caused by the gravity of its planets orbiting. The wobbles indicate definitely 2 planets and possible 3 at HD 1461. According to one of the discoverers, there appear to be small planets (less than Neptune’s mass) orbiting about half of the stars in the Sun’s neighborhood.
Exoplanet imaged – Yet another exoplanet has been directly imaged, raising the total to 10, just over a year after the first was imaged in visible light. The other 400 known exoplanets have been found by methods other than imaging them. The newly imaged planet orbits a Sun-like star GJ 758. The exact mass is not known, though it is at least 10 times that of Jupiter, so there is a possibility that the object is a small brown dwarf rather than a large planet. It orbits its star at about the same distance as Neptune orbits the Sun. It is about 600° F, which is attributed to its internal heat from having formed recently. It is too far from its star to have been heated by it. The image was taken with an adaptive optics instrument on the Subaru Telescope in Hawaii.
Retrograde exoplanet – A second exoplanet (designated HAT-P 7b) has been found to revolve about its star in the direction opposite to the star’s rotation. The method of determining this was the same as the 1st: see what part of the spectrum of the star is blocked at the beginning and end of transit of the planet in front of its star. The redshifted part is from the side of the star rotating away from us. Due to uncertainties in the measurement, it is possible that the planet does not revolve in the retrograde direction, but if so, then it has to be in a very steeply inclined (relative to the star’s equator) orbit. Planned observations by the Kepler spacecraft should be able to determine which is the case. In either case, that is a very unusual orbit. Planets form from clouds of material swirling about a star in the same plane and direction as the rotation of the star. So a retrograde or steeply inclined planet would require a major disturbance since it formed.
Possibly not an exoplanet – I reported here in July that after about 50 years of attempts to find exoplanets with astrometry, there was finally a success. Astrometry is measuring the location of a star very precisely, and in the case of planet search, looking for wobbles in that location. However, another astronomer using the radial-velocity method has been unable to find a planet at the same star. Either astrometry made yet another error in attempting to find planets, or the radial-velocity measurements just made were not sensitive enough. The debate will continue.
Spitzer (infrared space telescope) contributed to the discovery of the youngest brown dwarf known. Brown dwarfs generally fall between planets and stars in terms of their masses and temperatures. It has been debated whether brown dwarfs form the same way stars do, or as planets do. The newly discovered brown dwarf appears to have formed as stars do, adding one piece of evidence toward that theory. Its age was determined from temperature and brightness. It is being called a proto brown dwarf, since it is still in the process of forming. It was hidden in the cloud that formed it, but infrared light was able to penetrate that cloud. A second young brown dwarf was also found in the same cloud.
WISE (infrared survey space telescope) was launched December 14, and after a month of calibration is planned to map the entire sky 1.5 times over. Its critical parts are cooled with a frozen block of hydrogen, which should last for about 10 months. WISE will see the sky with sensitivity and resolution far better than the last infrared sky survey, which occurred 26 years ago. It is expected that WISE will detect many planet-forming disks, hundreds of thousands of asteroids, and hundreds of millions of stars and galaxies. The atlas of objects that WISE sees should provide astronomers with data for years. The atlas will also help plan observations with the planned James Webb infrared space telescope, which is far more sensitive, but sees such a small portion of the sky that it will never come close to observing the entire sky.
Strange supernova explained – After examining old images of the area, astronomers found that supernova 2008iy took 400 days to rise to peak brightness. No other supernova had taken over about 100 days. Most Type II supernovas rise in about a week. A new paper appears to explain the slow rise. The unusual spectrum of 2008iy showed that it was a Type IIn, a core collapse of a large star, with narrow spectral lines. There is evidence for a strong pre-supernova stellar wind, which produced clouds of matter surrounding the star. These clouds initially hid the supernova from view, but were eventually broken through by the force of the explosion. As this happened, apparently over 400 days, the supernova came into our view. This scenario matches the spectra and the rise time. Pre-supernova mass loss sufficient to obscure the explosion could probably come from only an LBV (luminous blue variable) star.
STEREO (twin solar space telescopes) – In the past what appear to be huge waves of hot plasma traveling across the Sun have occasionally been seen. Their sheer size prompted disbelief among many astronomers, and the phenomenon has been theorized to be simply shadows of mass ejections, which were known to be that large. STEREO observed such a wave from its 2 locations, providing a 3-dimensional view, and the huge waves are real. The waves have been given the name fast-mode magnetohydrodynamical waves, or for short MHD waves or solar tsunamis. STEREO’s tsunami moved at 560,000 mph and was 60,000 miles high. It was observed to hit a prominence and knock it about.
Fermi (gamma-ray space telescope) has detected a major flare up in gamma rays from the blazar 3C454.3. A blazar is a quasar whose brightness varies wildly. It is about 10 times as bright in gamma rays as it was before the flare, and is now the brightest gamma-ray object in the sky. The blazar has also brightened significantly in infrared, X-ray, radio and visible light. This blazar has been seen to flare up 3 previous times, but this is the brightest in gamma rays. It is not the brightest of the flare ups in all wavelengths though. The cause of blazar flare ups has not been determined; it may be shifting of its jets more toward us, shock waves, more material falling into its black hole, or some other cause.
Fermi has also detected flares of gamma rays in the binary system Cygnus X-3. This system is a microquasar, that is, a stellar mass black hole that has formed jets like the quasars found in the centers of some distant galaxies, but much smaller. This is the first detection of a microquasar in gamma rays, though they have been seen in many other wavelengths of light.
Star formation – Using the Very Long Baseline Array of radiotelescopes for a 2-year look at “proplyds”, or planet-forming disks, in Orion has provided astronomers with a high-resolution time-lapse movie revealing the process of how a massive star forms. The VLBA sees thousands of silicon monoxide gas clouds that are masering (like a laser but at microwave wavelengths), which are often associated with star formation. The masers’ motion was tracked periodically to make the movie. The movie reveals signs of a rotating accretion disk, where gas is swirling closer to the protostar at its center. It also shows material flowing outward perpendicular to the disk in two large cones of gas. Intriguingly, the outflow stream curve as they leave the disk. This is key evidence that magnetic fields may be bending the gas motions close to the protostar. It is not known whether the magnetic fields originate in the star or the accretion disk. Future observations by larger telescopes may be able to distinguish between these.
Star formation and quasars – A quasar (designated HE0450-2958) has been caught causing star formation in a galaxy. Furious star formation is occurring in the path of the quasar jet. That quasars could cause star formation in their surrounding galaxies has been postulated. But this quasar is causing star formation in a nearby galaxy. Further, the deepest images, even in infrared that penetrates obscuring clouds, fail to show a galaxy surrounding the quasar. Theorists had proposed that interstellar gas could possibly collapse into a black hole, the core of a quasar, without forming a galaxy about it, and this appears to be the case with this quasar.
Big Dipper – Astronomers observing with the Palomar Hale Telescope using adaptive optics and an occulting device to block out bright star light managed to image a dim companion star to Alcor, one of the stars of the Big Dipper. Alcor’s neighbor, Mizar, has long been known to be composed of 4 stars orbiting each other, but Alcor was thought to be single. The new discovery is a red dwarf star. It was determined to be a companion to Alcor, not just a background star, by observing its parallactic motion, the apparent motion caused by the Earth orbiting the Sun, and the motion was found to match Alcor’s. It was thought that Alcor and Mizar are too far apart for their gravity to be holding them in orbit about each other, but the added mass of Alcor’s companion may negate this, making it a 6 star system.
Flyby anomaly – Since the early 1990s scientists have noticed that some spacecraft that flyby the Earth experienced a very small, but measurable, unpredicted change in speed. So they were carefully watching the flyby of the Rosetta spacecraft on November 13. This was the 3rd flyby for Rosetta, but only the 1st showed the anomaly. Several theories, some bizarre, have been proposed to explain the anomaly. They include tidal effects, atmospheric drag, pressure from reflected radiation, dark matter, dark energy, and General Relativity. But none of them seems to fit all the observations. The Rosetta flybys made fitting the observations even more difficult.
Hayabusa (Japanese asteroid sample return mission) – When we last checked on Hayabusa, it was on its way back toward Earth and the 3rd of its 4 ion thrusters had failed (the chemical rocket system had long ago failed). Controllers were hesitant to turn on the 4th, since voltage spikes seemed to be destroying the thrusters. Spacecraft engineers discovered that 2 of the failed thrusters, if both turned on, would form one complete thruster, since different parts had failed. The only disadvantage is that it uses twice as much fuel and electricity as one thruster, but with no more force produced. But there is enough spare fuel and electric power. So Hayabusa is back on track to meet Earth (Australia specifically) next June. Then we will find out if the failures during sample recoveries prevented some or all of the sample from being gathered. The other earlier failures were overcome by, among other things, using backup systems and taking a different orbit back to Earth, resulting in a substantial delay.
Largest telescope – 35 radio telescopes on 6 continents (and some off continents) were linked together to act as one, forming the largest telescope ever, and made observations for 24 hours. The previous record was 23 radiotelescopes linked. The reason for the link was to make the most accurate measurements ever of the locations of more than 200 quasars scattered over the entire sky. This will be used to make a frame of reference for the precise location of all astronomical objects, not just by radiotelescope observations, but in all wavelengths.
Instant AstroSpace Updates
Observing Centaurus A, a galaxy known to have suffered a merger, in infrared using the New Technology Telescope in Chile, astronomers found a large ring of recently formed and still forming stars near the center of the galaxy. It is hidden in visible light by a huge dust lane.
Terzan 5, long thought to be a globular cluster, has been found to have stars of 2 different ages, while globulars generally have only 1 age of stars. Thus it is probably instead a dwarf galaxy that got grabbed by the Milky Way.
Observations of nova V445 Puppis show that it is quite bright for a white dwarf and has been depleted of hydrogen and therefore it may be nearing the point where it becomes a Type Ia supernova. That is where a companion star dumps enough material onto a white dwarf star so that it exceeds the limit of what such a star can support and it implodes.
There was no doubt that the Large Hadron Collider, which is mostly in Switzerland, was the largest particle collider in the world (17 miles around), but now it is the most powerful, since it was run at 1.18 teraelectron volts (TeV) (the previous record was 0.98 at Fermilab). This is just tune up, as regular operations will proceed up to 7 TeV next year.
Hubble Space Telescope (HST) has repeated its ultra deep field image but using the new more sensitive camera (WFC3) and doing it in infrared instead of visible light. Even dimmer, more distant galaxies were found.
The WFPC 2 camera that was removed from HST during the recent service mission to make space for the new and improved WFC3 was returned to Earth and is going on display in the Smithsonian Air and Space Museum. WFPC 2, with its correction for the error in the shape of the primary mirror, saved HST. WFPC 2 spent 15 years in space and took over 135,000 images.
The ALMA radiotelescope, located high in the Andes Mountains, made its first observation, using the 2 completed antennas of the 66 under construction. It achieved interferometric lock on a distance quasar at submillimeter wavelengths.
