AstroSpace Update – February 2010
AstroSpace Update
February 2010
Gathered by Don Lynn from NASA and other sources
Cassini (Saturn mission) has imaged a flash of sunlight reflecting from a lake (of methane) on Saturn’s moon Titan.
Scientists have been waiting to take this image to allow the seasons to change at the planet, causing sunlight to strike far northern areas of both Saturn and its moons. The image was taken in infrared, since it penetrates Titan’s clouds, while visible light does not. Astronomers were able to pinpoint the reflection seen to the southern shoreline of a lake called Kraken Mare, which covers an area larger than the Caspian Sea on Earth.
A new paper using data from Cassini says that blobs of warm ice periodically rise to the surface of Saturn’s moon Enceladus and churn the ice crust. The claim is that we happen to be exploring there during one of those periods, which explains the strange hot spots of the Tiger Stripe region of Enceladus, and possibly explains the cracks and geysers too. The study shows that the heat release and argon gas release currently measured cannot be sustained over geological time periods, so we must now be in an unusual time. Such behavior probably occurs only 1-10% of the time.
Lunar Reconnaissance Orbiter (LRO) has found an unexpected lunar radiation source and detected the coldest known location in the solar system. Since June, LRO has been mapping the moon, in part to find suitable landing sites for suture human expeditions. The Sun’s sunspot and related activity expand the protection of the solar system from cosmic rays. Since we are at a solar activity minimum, more cosmic rays than usual penetrate the solar system. LRO found that apparently cosmic rays hitting the lunar surface interact with surface material to produce a secondary source of radiation emanating back into space. LRO also found that one crater near the lunar south pole, Hermite Crater, reaches minus 415 °F, the coldest temperature yet measured in the solar system. This occurs deep within the crater where sunlight never penetrates.
Kepler (planet-searching space telescope) has discovered 5 exoplanets (planets outside our solar system), which have now been confirmed with ground-based observations. All are substantially less dense than gas giant planets in our solar system. One is the least dense planet known, about the density of styrofoam. Another of the 5 is quite similar to Neptune in size. All are close to their stars, and orbit about them in rather short periods (3.3 to 4.9 Earth days). All orbit stars hotter than our Sun. Their stars, being so close and hot, are heating the planets to temperatures of 2200 to 3300 °F, which is hotter than molten lava. They were all found in data taken during the first 6 weeks of operation. The Kepler data contains about 100 planetary candidates so far that are being further analyzed to confirm that they are indeed exoplanets. Also a number of binary stars, oscillating stars, and pulsating stars are showing up in the data. So we should see many more discoveries in coming months.
Kepler also found some Jupiter-sized objects orbiting stars where the planet-like object is hotter than its star. The Kepler science team has no idea what these objects are.
Small exoplanet – Astronomers have detected an exoplanet that is only 4 times the mass of Earth, making it the 2nd smallest exoplanet known. It orbits the star HD156668 every 4 Earth days and is about 80 light years from us in Hercules. It was found using the radial velocity method: measuring the wobbles of its star caused by its gravity.
Exoplanet spectrum – Astronomers have obtained the 1st direct spectrum of an exoplanet. The few times that an exoplanet spectrum has been previously obtained, it was done by subtracting the spectrum of the planet’s star (taken during eclipse of the planet) from the spectrum of the combined star and planet. Until now, technology did not permit separating a planet and its much brighter and very close star. The planet is 1 of 3 gas giants known to be orbiting the star HR 8799. All are farther from their star than Uranus is from our Sun; that distance helped separate the planets in the new observations. The spectrum was made using the Very Large Telescope in Chile with adaptive optics to increase resolution. The spectrum did not fit theory of a gas giant atmosphere. The first guesses are that the spectrum might be explained with less methane, more carbon monoxide, and the presence of dust clouds.
Possible exoplanet – The exoplanet known as TrES-2b (so-named because the TrES planet search program found it 2nd) has the plane of its orbit almost exactly in our line of sight. Careful observations, started back in 2006, of the planet covering a tiny portion of its star’s light (transiting) have allowed determination of the size of the star, size of planet, its period of revolution, and the inclination of the orbit. Continued observations showed that the inclination and period are changing. Of the various factors that could cause these changes, a new paper suggests the most likely is that another planet is also orbiting the star, and is perturbing TrES-2b. A planet of about Jupiter’s mass and a period of 50 to 100 days would cause perturbations of the size seen.
Exoplanet frequency – Astronomers (and philosophers) have long wondered how common are planetary systems resembling our solar system. Even after finding more than 400 exoplanets, we still can’t answer this. The methods used to find exoplanets are sensitive to only certain types: massive, nearby, close to their star, large diameter, or other characteristics. So the planets found are not a representative sample. 2 characteristics of our solar system are 1) that it has 4 gas giants, and 2) those are spread from 5 to 30 AU from their star (an AU is the Earth’s distance from the Sun). One planet-finding technique is sensitive enough to find multiple gas giants at these kinds of distances from their stars, that being microlensing. In this technique, the brightening is detected that is caused when a massive object (such as stars or planets) pass in front of a more distant star, and focus the distant light through their gravity (a relativistic effect). The MicroFUN survey has now examined enough microlensing events that statistically it should have discovered 8 systems with multiple gas giants in roughly the range of distances as our solar system if every star in the galaxy had such planets. But it has discovered only one such case. Now one data point isn’t much on which to base an estimate, but that says that 1 star in every 8 has multiple gas giants at the distance range of our solar system. It is thought that multiple gas giants at those distances protect rocky smaller planets closer in to their star, at such distance as to be the right temperature for life. But no method of planet discovery is yet sensitive enough to find rocky planets about 1 AU from its star, so we will have to settle for now for an estimate of gas giants similar to our solar system.
Planets around massive stars – A team of astronomers examined more than 500 massive stars in one star forming region in Cassiopeia, using Spitzer and ground-based 2MASS data, to look for planetary dust disks. The stars were spectral type A or B, which generally are 2-15 times as massive as our Sun. About 10% of the stars had dusty disks, and about 1/3 of those had a central gap, characteristic of a Jupiter-class planet sweeping up part of the disk. This shows that planetary systems are reasonably common among this class of star. Most planet searches have looked around lower mass stars, more similar to our Sun. The research team suggested that all massive stars may begin their life with a sizeable dusty disk, but that they blow away the disk by light and stellar winds after just a few million years. This implies that planets must form fairly quickly around massive stars, or miss the window of opportunity for planets.
Hubble Space Telescope (HST) has broken the distance record for galaxies and discovered a population of compact ultra-blue galaxies. The newly found galaxies are so distant that their light left there 600 to 800 million years after the Big Bang, that is, about 13 billion years ago, so we are seeing them as they appeared long ago. They were found in the Hubble infrared ultra deep field image taken a few months ago. The faintest galaxies were found to be quite blue, apparently due to large numbers of massive stars, which shine blue-white, or due to the lack of dust, which reddens starlight. When the first galaxies formed, the gas out of which stars were made was essentially all hydrogen and helium (which the Big Bang produced) with extremely little heavier elements. It is believed that such gas deficient in heavier elements will form more massive stars than the gas clouds with even a sprinkling of heavy elements. Those heavy elements are made inside stars and supernovas, and are distributed into interstellar gas by stellar winds and the force of supernova explosions, but the distribution process is thought to take a billion years or longer. The newly found galaxies show that galaxies had started to form by about 500 million years after the Big Bang, at latest. The time when the first galaxies formed has long been in contention. The blue galaxies found are compact: as small as 1/20 the diameter and 1/100 the mass of our Milky Way galaxy. The masses were calculated and ages confirmed from observations made with Spitzer (infrared space telescope). The compact galaxies are the building blocks out of which later and larger galaxies formed. Finding earlier (more distant) galaxies and more precisely dating them will probably have to wait for the much larger James Webb space telescope, scheduled for launch in 2014.
Luminous Blue Variables (LBVs) are a rare class of extremely massive stars. Eta Carinae is perhaps the best-studied LBV. Many LBVs are shrouded by nebulosity because they throw off large amounts of mass. This makes it hard to discover LBVs. A new study of LBV nebulas in Spitzer space telescope data showed that they emit in 24 micrometer wavelength of infrared, but not other wavelengths that Spitzer uses. So the proposal is that looking for nebulas that show up in only that wavelength will be an easy way to locate more LBVs.
Blue stragglers are stars that should be the same age as the other stars in their cluster, but are too blue, hot and massive to be that age. The class was recognized more than a half century ago. Eventually it was concluded that a blue straggler is created by gaining mass later in the star’s life. But the controversy continues over how the mass is gained. A new study of blue stragglers in the globular cluster M30 concluded that some gained mass by sucking hydrogen from close companion stars, and some did so by colliding with another star. The 2 methods apparently produce slightly different properties in the stragglers. It appeared that a collapse of the core of the cluster 1 or 2 billion years ago led to collisions that produced stragglers. The core collapse also disturbed enough binary stars to start a family of stragglers due to hydrogen sucking. Another study, done on open cluster NGC 188, concluded there was evidence of both methods of producing blue stragglers, and of a third method: a star passes close to a binary, and causes the stars of the binary to merge. This study noted a strange case of a binary star, of which both components are blue stragglers. They can’t both have gained mass from the other, so how did this binary form? The study concluded the stragglers formed individually in separate binaries, and then a close encounter between the 2 pairs caused a swapping of partners. The blue stragglers in NGC 188 were found to spin much faster than average, so the study will continue to determine what the spin tells us.
Epsilon Aurigae is currently undergoing its binary star eclipse that occurs every 27 years. Because the eclipse takes far longer (about 2 years) than other binaries, it has long been believed that the eclipse is caused by a huge dust cloud, not by a star. Also, a brightening in the middle of the eclipse implies there is a hole in the dust cloud. But some of the details of further observations have not been explained. The 2 best theories (and there are more than 2) are: 1) the bright star is a massive supergiant, and the dusty disk surrounds a close pair of stars, 2) the bright star is less massive, and the dusty disk surrounds a single star. New observations from the Spitzer space telescope support the 2nd theory. It requires that the primary star is in its dying stages in order to get the observed spectrum with a less massive star. The Spitzer observations were tricky to make, since Epsilon is too bright for Spitzer’s camera. The minimum exposure was made (1/100 second) and the star was positioned across 4 pixel boundaries so as not to overload a single pixel. The eclipsing disk was detected, and the infrared signature implies that the particles in the disk are gravel-sized, surprisingly large for a circumstellar disk. The diameter of the disk was found to be 8 AU.
Betelgeuse – Using interferometry (combining light from 2 or more telescopes) a team of astronomers generated an image of the surface of the supergiant star Betelgeuse. It showed 2 huge bright spots and other features. The bright spots indicate convection, where hot regions rise up to the surface. They are about 900 °F hotter than average. The diameter of the spots is about the distance of Mars from the Sun. Though the star has been imaged before, this is the highest resolution yet obtained. Two different computer programs were used to generate the image from the interference patterns produced by the interferometer, and the resulting images agreed.
Supernova by merger – Research simulating the merger of 2 white dwarf stars showed the results matched a few previously observed supernovas (those favoring Latin plurals will use the term supernovae) with odd characteristics, particularly supernova 1991bg. That and others were curiously less luminous than is expected for a Type Ia supernova. Type Ia normally occurs when one star in a close binary pair dumps matter onto its companion white dwarf until it explodes. Most of the visible light from a Type Ia supernova is known to come from radioactive decay of nickel 56, which is produced during the explosion. The new simulations showed less nickel 56 is produced from the merger than from the material-dumping scenario, explaining the lower luminosity. The researchers believe that merger situations represent 2-11% of all Type Ia supernovas. Since Type Ia supernovas are used as the brightness standard for many cosmic distance measurements, it is important to know when one of them is not the standard brightness.
Suzaku (Japanese orbiting X-ray observatory) has discovered evidence of high-temperature fireballs in 2 supernova remnants, the Jellyfish Nebula (IC 443) and W49B, that should have cooled and lost the evidence of the high temperatures. The nebulosity left from supernovas that occurred thousands of years ago has cooled from its temperature of about 100 million °F that was generated by the shock wave of the supernova. But Suzaku’s observations found completely ionized (lost all electrons) silicon and sulfur atoms, and ionizing those requires much higher temperatures than exist there today. The scientists concluded that soon after the supernova, when the completely ionized silicon and sulfur had just formed, the cloud expanded so fast that by the time the elements had cooled enough to recapture electrons, the remnant was so thinly spread that the ionized atoms never again collided with any electrons. So the ions were left long after heat that produced them.
Particle ribbon – It was reported here in December that the IBEX spacecraft had discovered a ribbon of particle emission coming from beyond the solar system that wraps around much of the sky. The source has now been identified. It is simply a reflection. Particles from the Sun reflect off the magnetic field of the interstellar space outside the solar system. Inside the solar system, the Sun produces the predominant field. Charged particles from the Sun, when they leave the solar system and encounter the different magnetic field, go into orbit about magnetic field lines. Whenever a particle loses its charge (from colliding with an oppositely charge particle), it flies off perpendicularly to the field lines. Thus we see these particles coming at us perpendicularly to that field, which appears as a ring about the sky. The recent result from the Voyager spacecraft that indicates the magnetic field outside the solar system is stronger than previously believed was necessary to explain the strength of the particle ribbon.
Magellanic Stream is a flow of gas that stretches from the Magellanic Clouds (small satellite galaxies) to our Milky Way. It was discovered over 30 years ago. A team using various radiotelescopes has examined the Stream more deeply than before and found that it does not have gaps as was believed from older observations. It is 40% longer than previously seen, and is older (2.5 billion years) than previously thought. The newly determined age puts its beginning at about the time the 2 galaxies are believed to have passed close to each other. That event probably gravitationally created star formation, and the stellar winds and supernovas from the new stars threw material out that became the Stream.
Milky Way halo – Though our Milky Way galaxy is shaped like a flat spiral, its larger halo has long been known to be roughly spherical. About 70% of the mass of the halo is thought to be dark nonbaryonic (not protons and neutrons) matter. A new study of the streamer of material from the Sagittarius Dwarf Galaxy shows that the Milky Way halo must be a rather squashed sphere in order for the streamer to have acquired its current shape. Surprisingly the sphere is squashed in the directions near the Milky Way spiral arms, and is longer in the direction of the poles. The amount of squashing calculated was also found surprising. The researchers plan to apply similar calculations to other dwarf galaxies near the Milky Way to confirm their results.
Earth’s magnetic field – A new study has confirmed previous theoretical predictions that the churning of molten metals that make up Earth’s liquid outer core is slowly being stirred by a complex but predictable series of oscillations. Scientists believe Earth’s magnetic field results from movements of molten iron and nickel within the outer core. This study used historic surface magnetic field data from back as far as 1840, combined with the latest satellite magnetic data. A model was proposed that the outer core rotates as a series of cylinders, with oscillations originating at the outside of the core and traveling inward. Then a computer program tried the model with different oscillation frequencies until the predicted field matched the observations. 4 robust frequencies were found, with periods ranging from 28 to 85 years, with weak indications of 2 more frequencies.
Interstellar cloud – The solar system is passing through an interstellar cloud of hydrogen and helium that differs in density from what theory predicts should occur. A study of data from Voyager showed that the magnetic field in interstellar space, outside the Sun’s magnetic zone, is stronger than predicted. In fact it is just strong enough to support the density found in the cloud that we are passing through, solving the mystery.
Spirit and Opportunity (Mars rovers) celebrated 6 years of roving Mars during January. Spirit is still stuck in soft soil. Rover controllers are considering a plan to dig one end in deeper, thus tilting it toward the winter Sun, to improve its chances of getting enough power from the solar panels to survive the oncoming Martian winter. Further efforts to spin out of the soft soil (early such efforts did not succeed) are also being considered. Plans are being made for what types of science Spirit can continue doing even if it is not freed from the soft soil.
Opportunity has been sitting by a rock called Marquette Island since early November. The rover has been conducting a thorough examination of the rock, including drilling a shallow hole in it to see and measure below the surface. When finished, the rover will resume driving toward Endeavour Crater, still several miles away. Near the end of December the odometer read 11.76 miles traveled since landing.
Phoenix – Beginning Jan 18, Mars Odyssey orbiter began listening for possible radio transmissions from the Phoenix Lander, which completed 5 months of studying an arctic Martian site in November 2008. Its mission was ended when it got too cold and dark for the lander to operate. It is expected that the severe Martian winter permanently damaged Phoenix, but in case the lander survived Odyssey is listening. It is now light and warm enough for Phoenix to operate (if it were freshly landed). In February or March, Odyssey will send operating commands to Phoenix in case it is listening.
Joint Mars plan – The new joint Mars exploration program of NASA and ESA (European Space Agency) is planning a Trace Gas Mission (TGM) orbiter to be launched in 2016. Its purpose is to study gases found in small concentrations in Mars’s atmosphere, in particular methane. The most likely sources of methane involve water or bacteria, and finding either of these would be a major discovery. Methane is known to be emitting from Mars, and TGM will try to pin down where and how much. TGM will be a combination of NASA’s previously planned Mars Science Orbiter and ESA’s ExoMars mission. If budget allows, a smaller lander will piggyback on the TGM launch. It would have few science instruments, but would principally test landing technology for future missions.
Mars Reconnaissance Orbiter (MRO) – A study of images from MRO has found areas near the Martian equator that appear to have been lakes about 3 billion years ago. Previous evidence of liquid water on the surface of Mars has been dated at 3.8 to 4 billion years ago. The new discovery implies that wet conditions on the planet persisted almost a billion years later than thought. The MRO images show depressions that in previous images could have been several things other than lakebeds. But MRO’s better resolution showed channels between some of the depressions, indicating water flowed, making lakebed the most probable interpretation of the depressions. The lakebeds and channels resemble similar features found in Alaska and elsewhere on Earth that are known to be caused by melting permafrost. The lakebeds were dated by counting craters that were caused by meteorite impacts. The researchers plan to continue examining MRO images of equatorial regions to see how widespread these lakebeds are.
SOFIA – Would you open the door to a jumbo jet while flying at 250 mph? NASA did. Under the door was their 2.5-meter (98-inch) SOFIA infrared telescope, and they wanted to test if the plane would fly and the telescope would withstand the experience with the door open. All went well. First light through the telescope while flying is scheduled for April, and full operations are to begin in the fall. Most wavelengths, or colors, of infrared are blocked by the Earth’s atmosphere, but when SOFIA flies at 40,000 feet, it will be above essentially all of that problem. Engineers believe that they have designed the telescope mounting so that it will track stars perfectly during a bouncy airplane ride with the door open. They also believe that the baffles around the door will produce smooth airflow past the telescope so that turbulence will not interfere with the image quality. Testing of this is proceeding.
Instant AstroSpace Updates
An extremely metal-poor star, with only 0.00025% of the iron found in the Sun, was discovered in the Sculptor dwarf galaxy. Very metal-poor stars are believed to be among the first stars formed after the Big Bang.
Fermi (gamma-ray space telescope) has continued to find millisecond pulsars (those spinning more than 100 times per second), due to their often emitting brightly in gamma rays. It has been proposed that continuous monitoring of the timing of pulses from millisecond pulsars would be able to detect gravitational waves.
A new computer program simulated the development of the universe over 13 billion years and for the first time produced the variety of galaxy types in the right relative numbers as seen in actual observations of the nearby universe. The simulation used dark energy and dark matter in its behavior.
New Horizons (Pluto mission) moved closer to Pluto than Earth on December 29; the halfway point along its orbit to Pluto will be reached February 25, and the halfway point in travel time in mid-October. Pluto flyby is summer 2015.
Scott Parazynski, retired astronaut, borrowed a moon rock from NASA that came from the Sea of Tranquility (Apollo 11 mission), and carried it to the top of Mount Everest, highest point on Earth. That moon rock and a rock from the Everest summit will be taken to the International Space Station for permanent display there in the Tranquility Module.
NASA has selected 3 proposals as candidates for their next mission in the solar system: 1) a probe of Venus’s atmosphere and crust, 2) a sample return from a near-Earth asteroid, 3) a sample return from the Moon’s south polar region. After further study, one of these will be selected for launch by 2018.
