A helium balloon on the moon might as well be made of lead. For any balloon to stay aloft in any atmosphere, the gas inside it must be lighter than the surrounding air.
Ultralight helium has no trouble climbing in Earth’s atmosphere, which consists mostly of heavy molecular nitrogen and oxygen. “But on the moon, there is no air, so there’s nothing for the helium to rise above,” says Marc Rayman, an engineer at NASA’s Jet Propulsion Laboratory. Unable to escape even lunar gravity, which is one sixth that of Earth’s, the balloon would plunge to the ground.
Try throwing a birthday party on the International Space Station, and you’ll run into the opposite conditions. Because atmospheric pressure in the station is kept the same as at sea level on Earth, a helium balloon would have the support it needs to float, but with almost no gravity on the station, there is no force to push up or down on the balloon. “It would just hang there, the same as if you let a hammer go,” Rayman says.
If you’re looking to throw an extraterrestrial fiesta for an astronaut, book a spot on Mars. The thin air on the Red Planet is still heavier than at the highest altitudes on Earth where balloons have floated. That, combined with gravity that’s about a third of Earth’s, would send a helium balloon on Mars up and away.
The fourth planet from the Sun, just past the Earth. Often called the 'Red Planet', due to its vivid colour.
REASONS TO VISIT
See the longest ever canyon system, stretching over 5,000km (3,100 miles)
Visit the Solar System's largest volcano - over 50 times bigger than those on Earth
Decide for yourself whether the Red Planet once contained life
WHAT TO SEE
Mars has some of the most spectacular scenery in the Solar System.
Valles Marineres A giant canyon system stretching over 5,000km (3,100 miles) along the equator with an average depth of 6km. See if you can spot the erosion channels that could reveal the planet's watery past.
Olympus Mons The largest volcano in the Solar System. Reaching 27km (17 miles) high and 700km (435 miles) across. But don't be afraid - this monstrous volcano is now extinct, so your visit will be a safe one.
The face In 1976, Viking Orbiter 1 sent pictures of a very unusual rock formation. When the Sun strikes Mars at a certain angle, the shadow looks like a human face.
Is this proof of alien intelligence at work? Or is it just chance that the rugged surface of Mars conjures up this image? Until there is more evidence, you will have to decide for yourself.
LOCAL HISTORY
It's usually claimed that Mars was named after the Roman god of war because of its angry red colour. But early on in the Roman empire, Mars was worshipped as a god of growth and fertility.
SPOTTING MARS FROM THE EARTH
Mars' red colour, though more pronounced when seen through a telescope, is still noticeable with the naked eye.
Mars can often be spotted from Earth. Usually it travels across the sky from east to west. However, for 70 days of its two year orbit, it reverses direction across the sky. This is the best times to observes Mars, because it's at the closest point to Earth.
TRAVEL INFORMATION
Journey time · 5.25 Earth months 1 Martian year · 2.11 Earth years Contacting home · Time lag = 25.4 minutes
Before you leave Mars is closer in temperature to Earth than any of the other planet in the Solar System. But don't let this catch you off your guard. Mars' weather is even more unpredictable than our own.
We recommend a summer visit, when the temperature can reach a pleasant 20ºC. But keep an eye on the weather forecast! Storms can sweep across the whole planet. Within days, the temperature can plummet by 20 degrees.
Travellers in the winter months should note that Mars can reach a bitter -140ºC.
One final word of warning - make sure you are prepared for dust storms. Tornadoes as large as eight kilometers high have been seen causing havoc across the Martian landscape.
When you arrive Your first decision when you arrive will be which hemisphere to head for. The southern hemisphere is higher, and has a more rugged landscape.
The northern hemisphere lies an average of five kilometres lower. We know that the surface there is younger as there are fewer impact craters.
There is no evidence of plate tectonics on Mars. This means that growing volcanoes aren't disrupted by surface movements. So they can grow 100 times larger than on Earth, like Olympus Mons. But don't worry, the volcanoes on Mars aren't active.
A PLANET orbiting a nearby star is the best candidate yet for an alien world made almost entirely of liquid water. The discovery suggest that "super-Earths" are a much more diverse bunch than we suspected.
Super-Earths weigh up to 10 times as much as our planet. They may be among the most common types of planet in the Milky Way, and some could turn out to be cosy places for life. Around a dozen have been found, but for the most part, astronomers have been unable to pin down their properties because they don't pass in front of, or transit, their host stars as seen from Earth. Transits reveal a planet's size, allowing its density and composition to be inferred.
Earlier this year, the CoRoT spacecraft found the first transiting super-Earth, calledCoRoT-7b . Broiled by its host star, the planet may be a rocky body covered in pools of lava on the side that always faces the star.
Now, astronomers have found the second transiting super-Earth around a nearby red dwarf. Called GJ 1214b, it is about 19 times as large as Earth by volume but only 6.6 times as massive. Such an object could be composed primarily of water - likely in liquid form - with a modest amount of rocky material at its core. Calculations show it must also have an atmosphere (see diagram). Its proximity to the red dwarf, however, makes it slightly too hot to be habitable
The differences between the two planets suggest that super-Earths form in many different ways, says David Charbonneau of Harvard University, who led the team that discovered GJ 1214b. If it is a water world, "it could be the first clear example of a whole new population of exoplanets", says Sara Seager of the Massachusetts Institute of Technology.
Theoretical models by Seager and student Leslie Rogers show that such a planet could form if it began life much farther from its star. The lower temperatures there would have led to an ice-rock composition similar to Jupiter's moon Ganymede. Later, as the planet shifted into a tighter orbit, it would become a water world with a steamy atmosphere. Other possibilities include a small rocky planet with an implausibly vast atmosphere possibly replenished by volcanic activity.
Baby black holes are puny compared with their humongous cousins at the centres of galaxies, but their birth may spew out the universe's mightiest particles.
Subatomic particles are routinely detected smashing into Earth's atmosphere at incredibly high energies, but the origin of these ultra-high-energy cosmic rays (UHECRs) remains a mystery. Some have argued that energy released by the collapse of a massive single star to form a black hole might produce the UHECRs, but the rate of such events is too low.
Todd Thompson at Ohio State University in Columbus and his colleagues argue that UHECRs may instead originate in the merger of two types of dead star, which gives birth to a black hole. They base this conclusion on the discovery of a system destined for such a merger by a team led by Carles Badenes of Princeton University. Badenes's team examined archival observations and found a white dwarf and neutron star orbiting one another extremely closely. They are spiralling toward each other, and should merge to form a black hole within 500 million years.
Thompson and colleagues point out that Badenes's team probed only a tiny fraction of the galaxy before finding this system, suggesting such doomed pairs are abundant. These collision events should be about 100 times more common than collapses of individual stars, the team calculates (arxiv.org/0912.0009).
"These objects are certainly very interesting," says Miguel Mostafá of Colorado State University, Fort Collins, who is not a member of either team, but he cautions that the rate of mergers is still highly uncertain.
NASA's latest space surveyor should be able to peer at distant galaxies and uncover dim objects right in our own celestial backyard
Nestled into the payload of a Delta 2 rocket at Vandenberg Air Force Base in California is a satellite that should open new targets for astronomical study both near and far. NASA's Wide-field Infrared Survey Explorer (WISE), slated for launch no earlier than 6:09 A.M. Pacific Standard Time on December 11, is charged with mapping the sky in the mid-infrared to create an atlas of objects whose emitted light is invisible to human eyes and largely absorbed by Earth's atmosphere.
The international Infrared Astronomical Satellite, the most direct predecessor to the $320-million WISE, was launched more than 25 years ago. With the increases in technology and astronomical know-how since then, a bounty of new objects may await discovery by WISE, from distant galaxies whose optical light is dwarfed by their infrared output to failed stars known as brown dwarfs, some of which may be closer to Earth than the star Proxima Centauri, the sun's nearest known neighbor.
"WISE is going to survey the entire sky inthe mid-infrared —that's wavelengths about five to 33 times longer than the red light you can see," explains the mission's principal investigator, astronomer Edward Wright of the University of California, Los Angeles. "By studying these longer waves, we can look at the sources of light that are cooler than, say, the lightbulb filaments or the sun that normally produce the light that we see."
The satellite will circle Earth in a polar orbit (flying over both poles), following the so-called terminator—the divider between day and night on the planet below. By maintaining that orientation, WISE can point its telescope away from Earth and keep the sun on one side, allowing the spacecraft to be shielded from solar radiation by its sunshade. WISE's longer-wavelength detectors will be cryogenically cooled to just 8 kelvin, or about –265 degrees Celsius; warm instruments can contaminate infrared observations with their own radiated heat.
It will take half an Earth orbit around the sun, or half a year, to map the whole sky. With enough cryogen for 10 months of flight, WISE should be able to complete one full survey before doubling up observations on half of the sky. Six months after the spacecraft runs out of coolant for its instruments, a preliminary data set should be released to astronomers.
In the course of the mission, Wright predicts, "we'll see hundreds of millions of sources, and we'll find millions of brand-new objects that nobody knew existed." WISE will also help constrain the threat of near- Earth asteroids, many of which are already catalogued but whose size—and hence potential for harm—can be difficult to gauge from their reflectance of optical light alone.
ButMichael Skrutskie, a University of Virginia astronomer and a member of the WISE science team, is especially interested in the satellite's ability to pick out previously unknown brown dwarfs, objects larger than planets but too small to sustain nuclear fusion of hydrogen. Because they do not burn bright like normal stars, brown dwarfs are difficult to spot, but they radiate enough heat to show up in the infrared.
"If you look at the brown dwarf discoveries to date, the coolest ones found—and this is largely because searches have gone on in the near-infrared almost exclusively—are about 600 or 650 degrees kelvin," Skrutskie says. "You know there's a population of cooler brown dwarfs out there; we're just seeing the tip of the iceberg now. WISE is designed to find those."
Skrutskie was principal investigator of the Two-Micron All-Sky Survey (2MASS), a ground-based observation campaign taken in shorter (warmer) infrared wavelengths than those WISE will probe. So he is familiar with the role that sky maps generated by surveys play in driving further research. "Sky surveys are in some ways fundamental to opening up new classes of objects to investigation with larger telescopes," he explains.
One of those telescopes is Herschel, a space-based infrared observatory launched in May by the European Space Agency in collaboration with NASA. Data from WISE may generate proposals for telescope time on Herschel for more detailed follow-up observations, says Paul Goldsmith, project scientist for Herschel at the NASA Jet Propulsion Laboratory (JPL) in Pasadena, Calif. (Goldsmith's JPL colleagues will manage ground operations for WISE;Utah State University's Space Dynamics Laboratory in North Logan, Utah, designed and built its instrumentation, and Ball Aerospace in Boulder, Colo., built the spacecraft itself.)
Like the Hubble Space Telescope, which also has infrared capabilities, Herschel is a pointed instrument, not a wide-view surveyor like WISE. Herschel boasts a telescope even larger than Hubble's and roughly nine times the diameter of that on WISE. "You have to know where to look with Herschel," Goldsmith says.
"They could turn up some really exciting stuff—anything from brown dwarfs to galaxies," Goldsmith says of the WISE team. "There will be a lot to keep astronomers busy, but that's a good problem to have."
Indeed, Wright says, one of the most exciting aspects of the WISE mission is its potential to tap into the unknown. His colleague Skrutskie agrees. "It's the Forrest Gump approach, right?" Skrutskie says. "The sky is like a box of chocolates—you never know what you're going to get."
A specialized camera on a telescope operated by U.K. astronomers from Liverpool has made the first measurement of magnetic fields in the afterglow of a gamma-ray burst (GRB). The result is reported in the Dec. 10 issue of Nature magazine by the team of Liverpool John Moores University (LJMU) astronomers who built and operate the telescope and its unique scientific camera, named RINGO.
The burst occurred January 2, 2009. NASA's Swift satellite observed its position and immediately notified telescopes all over the world via the Internet. When it received the trigger from Swift, the robotic Liverpool Telescope on the island of La Palma in the Canary Islands automatically swung to observe the burst. Its special camera employs a spinning disk of Polaroid -- similar to the material used in sunglasses.
"By observing how the brightness of the GRB varied as we spun the Polaroid, we could measure the magnetic field in the burst," explained Iain Steele, Director of the Liverpool Telescope.
"This important result gives us new insight into the physics of these remarkable objects and is a testament to the close collaboration between observers, theoreticians and technologists in the Liverpool and NASA Swift teams," added LMJU team leader Carole Mundell. "It's incredible to think that the GRB discovery and our measurement process -- from first detection and notification by NASA's Swift satellite to the polarization measurement using RINGO on the Liverpool Telescope -- took place completely automatically within less than three minutes and with no human intervention!"
"This breakthrough observation gives us the first measurement of magnetic fields in the afterglow of a GRB," said Swift lead scientist Neil Gehrels, Swift lead scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.
Gamma Ray Bursts form when the core of a massive star collapses or when two neutron stars merge together. The resulting explosions are the brightest events in the universe and vastly outshine entire galaxies containing hundreds of billions of stars. NASA's Swift satellite sees about 100 of these events each year, triggering ground-based follow-up by observations across the globe.
Polarization is one of the least-observed properties in astronomy. This finding opens the door to understanding the role of magnetic fields in some of the most powerful events in the universe.
"These very interesting observations raise the possibility that gamma-ray bursts are not fireballs as usually presumed but are powered and collimated by an organized electromagnetic field," said Roger Blandford, Director of the Kavli Institute of Particle Astrophysics and Cosmology at Stanford University, California, commenting on the result's importance. "It will be very interesting to see if there are similarities in observations of other kinds of cosmic jets."
ESA's XMM-Newton X-ray observatory is celebrating its 10th anniversary. During its decade of operation, this remarkable space observatory has supplied new data for every aspect of astronomy. From our cosmic backyard to the further reaches of the Universe, XMM-Newton has changed the way we think of space.
On 10 December 1999, an Ariane 5 blasted off from Europe's Spaceport in Kourou, French Guiana, carrying the 10 m-long XMM-Newton satellite. It spent eight days manoeuvring into its operational orbit around Earth, a highly elliptical circuit that reaches a third of the way to the Moon. XMM-Newton's three gold-coated mirror modules began focusing X-rays onto its five instruments soon afterwards. An optical monitoring camera allows astronomers to pinpoint their targets. What began as a steady stream of new data turned into a flood, with more than 2200 research papers now published based upon XMM-Newton's observations.
"10 years is a long time for a space mission; we have made progress in all aspects of astronomy," says Norbert Schartel, ESA Project Scientist for the mission.
X-rays from space are usually produced under the most extreme conditions, often from dramatic celestial events. They can be generated in the intense gravitational and magnetic fields surrounding celestial objects such as neutron stars and black holes, or when gigantic clouds of gas collide within clusters of galaxies.
XMM-Newton has excelled at studying black holes or, more accurately, their environment. By identifying X-rays given off by iron atoms, it has probed the way black holes twist the fabric of space-time around themselves. It has also revealed the way in which supermassive black holes grow and drive the evolution of the most massive galaxies in the Universe, and it has traced the development of the largest structures in space: galaxy clusters. It has tracked the production and dispersal of heavy chemical elements by exploding stars, and measured powerful magnetic activity coming from young Sun-like stars.
Closer to home, XMM-Newton has discovered that Mars has a vastly larger atmosphere than previously thought. The Red Planet's tenuous outer layer, known as its exosphere, extends to six times Mars' radius. It has shown that icy comets from the outer Solar System give off X-rays. Perhaps one of the most extraordinary results has been that XMM-Newton pinpointed a hot spot on a neutron star, 552 light-years away. The hotspot was just 60 m across, a minuscule patch to see so clearly from Earth orbit. The satellite then went on to make similar discoveries on two other neutron stars.
XMM-Newton has played its part in the study of dark matter, the hypothetical substance thought to outweigh normal matter by five to one. The favoured variety of dark matter would release X-rays or gamma rays if a particle decays. XMM-Newton has looked for these 'decay lines' in galaxy clusters but not found anything, helping theorists to constrain their ideas.
Today, XMM-Newton remains at the forefront of astronomy, supplying data to some 2000 astronomers around the world, who currently produce around 300 refereed papers every year. Every second of observing time is highly contested, with astronomers regularly requesting seven-fold the amount available every time the project team asks for new observing proposals.
As for the future, there is plenty left to study. The earlier Rosat telescope catalogued 125 000 X-ray sources, whereas XMM-Newton has studied only about 4300 of them. Even after its decade in space, the satellite remains in excellent shape. "Technologically, there's nothing to stop us continuing for another decade," says Schartel.
