- Planets Weighed Using Pulsar Flashes
- Vault Freezes Coral Cells to Preserve Them From Extinction
- Danish Volunteers Build Manned Spacecraft
Posted: 23 Aug 2010 03:43 PM PDT
The rotating corpses of massive stars can help scientists weigh the planets in the solar system. By carefully timing radio blips from spinning stellar leftovers called pulsars, astronomers have measured the masses of all the planets from Mercury to Saturn, plus all their moons and rings.
Until now, the only way to figure out the mass of a planet was to send a spacecraft past it. The spacecraft's orbit is determined by the gravitational oomph of the planet (plus whatever moons lay within the spacecraft's orbit), which in turn depends on the planet's mass. The new method is the first to let astronomers weigh planets from the comfort of Earthbound observatories.
"That's what's remarkable about this technique," said space technologist William Folkner of NASA's Jet Propulsion Laboratory, a coauthor of a study in the upcoming issue of Astrophysical Journal describing the technique. "I can't think of any other way to measure masses of planets from the Earth."
The new method relies on the clock-like regularity of a class of neutron stars called pulsars, the rapidly spinning remains of massive stars that died in supernova explosions. Pulsars shoot tight beams of radio waves into space that sweep across the sky like a lighthouse, so from Earth they appear to blink or pulse.
Because the Earth is always moving around the sun, the time it takes for these radio blips to reach us is always changing. To get rid of this effect, astronomers calculate when the pulse should reach the solar system's center of mass, or barycenter — the point around which all the mass in the solar system moves. But because the planets' arrangement around the sun is constantly changing, the barycenter moves around with respect to the sun, too.
To pin down the center of mass at a given time, astronomers use a special table of where all the planets are, called an ephemeris, plus values for the masses of the planets taken from previous space missions. If the masses are slightly wrong, then a regular, repeating pattern of timing errors appears in the pulsar data. For instance, if Jupiter's mass is a bit off, then an error appears every twelve years, once for every time Jupiter orbits the sun. Correcting the value for Jupiter's mass makes the error disappear.
"You can see that 12 year wiggle in timing of neutron stars," Folkner said. "That tells you how far the sun is from the solar system barycenter, which tells you what the mass of Jupiter is."
An international team of scientists used three different radio telescopes, the 1000-foot wide Arecibo telescope in Puerto Rico, the 210-foot Parkes telescope in Australia and the 328-foot Effelsberg telescope in Germany to time the blips from four different pulsars over a period of 5 to 22 years. They then used computer models to use the pulsars' times to calculate the masses of Mercury, Venus, Mars, Jupiter and Saturn.
The masses the team found are not as accurate as the best measurements from spacecraft flybys, but they're close. The measurement for Jupiter, for instance, was found to be 0.0009547921 times the mass of the sun. This value is more accurate than the mass determined from the Pioneer and Voyager spacecraft, and less accurate than, but consistent with, the value from the later Galileo spacecraft, which includes more decimal places.
"Our error bars are larger than those of these spacecraft measurements," said study coauthor Andrea Lommen of Franklin & Marshall College. "We are admitting freely that you should still use the mass of Jupiter measured from the spacecraft, but it's comforting to know that our measurement agrees with that."
The new method is also the first that can measure the masses of everything in a planetary system, including moons and rings.
"Spacecraft flybys don't tell us the mass of everything in the Jupiter system, only the parts inside the spacecraft orbit," Folkner said. "With this pulsar timing mechanism, we're sensitive to the entire system, including the moons that are outside the orbit of any spacecraft that have flown by."
The technique is actually a stepping stone to studying something even more exotic: ripples in spacetime called gravitational waves that were predicted by Einstein but have never been observed. The timing of pulsar blips should change slightly whenever a gravitational wave goes by, but in order to see these changes, astronomers have to subtract out all the other noise that could alter the pulsar's clock.
This study is "a graphic demonstration that you really have to understand the solar system really well if you're going to be able to confidently detect gravitational radiation," commented astronomer Scott Tremaine of the Institute for Advanced Study in Princeton, NJ, who was not involved in the new work. "If they can continue to develop these techniques to the point where they can detect gravitational waves, that will be a dramatically important event."
Image: The sun, Earth and Jupiter orbit a common center of mass. David Champion, MPIfR
Posted: 23 Aug 2010 11:55 AM PDT
In an effort to preserve the biodiversity of Hawaiian coral species, scientists at the University of Hawaii have created the first frozen coral cell bank — similar in concept to a seed bank for plants.
"Because frozen banked cells are viable, the frozen material can be thawed in one, 50 or, in theory, even 1000 years from now to restore a species or population," said biologist Mary Hagedorn of the University of Hawaii in a press release. "In fact, some of the frozen sperm samples have already been thawed and used to fertilize coral eggs to produce developing coral larvae."
Coral reefs are disappearing at an alarming rate due to warming, acidifying oceans and other types of human impact. Just last week, scientists reported that a spike in ocean temperatures off the coast of Indonesia is causing the most massive die-off ever seen in the region, already killing 80 percent of the coral species on several reefs. These types events are expected to get more frequent across the globe, with some scientists warning extinction of coral reefs is eminent within the next century.
Coral reefs cover less than a tenth of the ocean's surface but are home to a quarter of all marine species. Corals enable this diversity by building complex structures where many creatures can live and hide.
Globally, there are approximately 1000 known reef-building coral species. Corals are primitive animals most closely related to jellyfish. The types of coral that build reefs get their color and most of their energy from symbiotic algae living within their cells. When water temperatures get hotter than corals they experience coral bleaching, where they expel their symbiotic algae, turn bleach white, and often die.
One of the other major factors threatening coral reefs is the oceans becoming more acidic from increased carbon dioxide in the atmosphere. In more acidic water corals have difficulty secreting their reef-building calcium carbonate shell.
So far, the Hawaiian coral cell bank has frozen sperm and embryotic cells from mushroom coral (Fungia scutaria) and rice coral (Montipora capitata). They aim to store as many species of Hawaiian coral as possible.
The work is being funded by the Smithsonian, University of Hawaii, Morris Animal Foundation, and Anela Kolohe Foundation.
Images: 1) Fungia, one of the corals deposited into the frozen repository. Ann Farrell/ Hawaii Institute of Marine Biology at the University of Hawaii. 2) Hawaii Institute of Marine Biology at the University of Hawaii.
Posted: 23 Aug 2010 08:29 AM PDT
A team of Danish volunteers has built a rocket capable of carrying a human into space, and will be launching it in a week's time. The project, which has been funded entirely by donations and sponsorship, is led by Kristian von Bengtson and Peter Madsen.
The rocket is named HEAT1X-TYCHO BRAHE, and its first test flight will carry a crash-test dummy, rather than a human, so that the safety aspects of the design can be analyzed. It'll launch from a floating platform that the team has also built, which will be towed into the middle of the Baltic Sea by a submarine called Nautilus that the pair built as their last project.
The creators are members of the SomethingAwful web community, and have been posting pictures and answering questions there. In response to one question asking what the chances of the person inside dying are, they replied: "Unlike Columbia we're not moving at orbital speeds so 'dying a gruesome death burning up on re-entry' with our kit has a very low outcome probability."
Despite that, the rocket will still break the sound barrier, and subject the pilot (who is forced to stand inside the capsule) to considerable g-forces. As a result, the astronaut will only be able to move his arms, which will be able to operate a camera, the manual override functionality, the exit hatch, an additional oxygen mask and a vomit bag.
When the rocket hits the team's original target suborbital altitude of 150,000 meters (almost 500,000 feet, approximately 93 miles) and begins to descend again, parachutes will slow it and the team will track it with a GPS link and a "fast boat". The team said: "We should be able to receive a descent plot which can be used in projecting a splashdown ellipse pretty accurately, if we factor in wind speeds and so on."
The first test launch is slated for Aug. 31. The crew will set off from Denmark the previous day, as it takes about 36 hours of sailing to reach the site. The team's website is down at the time of writing, presumably due to the attention the launch is generating, but can be found at copenhagensuborbitals.com.
If successful, Denmark will be the fourth country to put one of its citizens into space, following the United States, Soviet Union and China, and the first in the world to do it without government funding.
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