Exoplanet Astronomers: 'Tilt-a-worlds' could harbour life

Tilted orbits such as those shown might make some planets wobble like a top that’s almost done spinning, an effect that could maintain liquid water on the surface, thus giving life a chance. 

Credit: NASA

A fluctuating tilt in a planet's orbit does not preclude the possibility of life, according to new research by astronomers at the University of Washington, Utah's Weber State University and NASA. In fact, sometimes it helps.

That's because such "tilt-a-worlds," as astronomers sometimes call them, turned from their orbital plane by the influence of companion planets, are less likely than fixed-spin planets to freeze over, as heat from their host star is more evenly distributed.

This happens only at the outer edge of a star's habitable zone, the swath of space around it where rocky worlds could maintain liquid water at their surface, a necessary condition for life.

Further out, a "snowball state" of global ice becomes inevitable, and life impossible.

The findings, which are published online and will appear in the April issue of Astrobiology, have the effect of expanding that perceived habitable zone by 10 to 20 percent.

And that in turn dramatically increases the number of worlds considered potentially right for life.

Such a tilt-a-world becomes potentially habitable because its spin would cause poles to occasionally point toward the host star, causing ice caps to quickly melt.

Rory Barnes

"Without this sort of 'home base' for ice, global glaciation is more difficult," said UW astronomer Rory Barnes.

"So the rapid tilting of an exoplanet actually increases the likelihood that there might be liquid water on a planet's surface."

John Armstrong

Barnes is second author on the paper. First author is John Armstrong of Weber State, who earned his doctorate at the UW.

Earth and its neighbour planets occupy roughly the same plane in space. But there is evidence, Barnes said, of systems whose planets ride along at angles to each other.

As such, "they can tug on each other from above or below, changing their poles' direction compared to the host star."

The team used computer simulations to reproduce such off-kilter planetary alignments, wondering, he said, "what an Earthlike planet might do if it had similar neighbours."

Their findings also argue against the long-held view among astronomers and astrobiologists that a planet needs the stabilizing influence of a large moon, as Earth has, to have a chance at hosting life.

"We're finding that planets don't have to have a stable tilt to be habitable," Barnes said. Minus the moon, he said, Earth's tilt, now at a fairly stable 23.5 degrees, might increase by 10 degrees or so. Climates might fluctuate, but life would still be possible.

"This study suggests the presence of a large moon might inhibit life, at least at the edge of the habitable zone."

The work was done through the UW's Virtual Planetary Laboratory, an interdisciplinary research group that studies how to determine if exoplanets—those outside the solar system—might have the potential for life.

"The research involved orbital dynamics, planetary dynamics and climate studies. It's bigger than any of those disciplines on their own," Barnes said.

Armstrong said that expanding the habitable zone might almost double the number of potentially habitable planets in the galaxy.

Applying the research and its expanded habitable zone to our own celestial neighborhood for context, he said, "It would give the ability to put Earth, say, past the orbit of Mars and still be habitable at least some of the time, and that's a lot of real estate."

More information: Paper: online.liebertpub.com/doi/abs/10.1089/ast.2013.1129

Exoplanet Orbits its star in 8.5 hours

Credit: CRISTINA SANCHIS OJEDA

In the time it takes you to complete a single workday, or get a full night's sleep, a small fireball of a planet 700 light-years away has already completed an entire year.

Researchers at MIT have discovered an Earth-sized exoplanet named Kepler 78b that whips around its host star in a mere 8.5 hours—one of the shortest orbital periods ever detected.

The planet is extremely close to its star—its orbital radius is only about three times the radius of the star—and the scientists have estimated that its surface temperatures may be as high as 3,000 degrees Kelvin, or more than 5,000 degrees Fahrenheit.

In such a scorching environment, the top layer of the planet is likely completely melted, creating a massive, roiling ocean of lava.

What's most exciting to scientists is that they were able to detect light emitted by the planet—the first time that researchers have been able to do so for an exoplanet as small as Kepler 78b.

This light, once analyzed with larger telescopes, may give scientists detailed information about the planet's surface composition and reflective properties.

Kepler 78b is so close to its star that scientists hope to measure its gravitational influence on the star.

Such information may be used to measure the planet's mass, which could make Kepler 78b the first Earth-sized planet outside our own solar system whose mass is known.

The researchers reported their discovery of Kepler 78b in The Astrophysical Journal.

In a separate paper, published in Astrophysical Journal Letters, members of that same group, along with others at MIT and elsewhere, observed KOI 1843.03, a previously discovered exoplanet with an even shorter orbital period: just 4 1/4 hours.

Saul Rappaport

The group, led by physics professor emeritus Saul Rappaport, determined that in order for the planet to maintain its extremely tight orbit around its star, it would have to be incredibly dense, made almost entirely of iron—otherwise, the immense tidal forces from the nearby star would rip the planet to pieces.

"Just the fact that it's able to survive there implies that it's very dense," says Josh Winn, an associate professor of physics at MIT, and co-author on both papers.

"Whether nature actually makes planets that are dense enough to survive even closer in, that's an open question, and would be even more amazing."

Earth's Other Moons

The path of a simulated minimoon that is temporarily captured by Earth. The object approaches Earth from the right along the yellow line and continues on its trajectory along the orange path and finally escapes capture along the red path to the upper right.

The size of Earth and the Moon are not to scale but the size of the minimoon's path is to scale in the Earth-Moon system.

Inset: Radar image of near-Earth asteroid 1999 JM8 made with NASA's Goldstone Solar System Radar in California and the Arecibo Observatory in Puerto Rico by a team of astronomers led by Dr. Lance Benner of NASA's Jet Propulsion Laboratory in Pasadena, California.

Minimoons are captured from the much larger population of near-Earth asteroids that pass close to Earth.

This two-mile-diameter asteroid is more than a thousand times larger than the biggest minimoons, but it shows the irregular shape and pockmarked surface expected on the much smaller minimoons.

Earth usually has more than one moon, according to a team of astronomers from the University of Helsinki, the Paris Observatory and the University of Hawaii at Manoa.

Our 2,000-mile-diameter Moon, so beloved by poets, artists and romantics, has been orbiting Earth for over 4 billion years. Its much smaller cousins, dubbed "minimoons," are thought to be only a few feet across and to usually orbit our planet for less than a year before resuming their previous lives as asteroids orbiting the Sun.

Mikael Granvik (formerly at UH Manoa and now at Helsinki), Jeremie Vaubaillon (Paris Observatory) and Robert Jedicke (UH Manoa) calculated the probability that at any given time Earth has more than one moon.

"Minimoons are scientifically extremely interesting," said Jedicke. "A minimoon could someday be brought back to Earth, giving us a low-cost way to examine a sample of material that has not changed much since the beginning of our solar system over 4.6 billion years ago."

They used a supercomputer to simulate the passage of 10 million asteroids past Earth. They then tracked the trajectories of the 18,000 objects that were captured by Earth's gravity.

They concluded that at any given time there should be at least one asteroid with a diameter of at least one meter orbiting Earth. Of course, there may also be many smaller objects orbiting Earth, too.

According to the simulation, most asteroids that are captured by Earth's gravity would not orbit Earth in neat circles. Instead, they would follow complicated, twisting paths.

This is because a minimoon would not be tightly held by Earth's gravity, so it would be tugged into a crazy path by the combined gravity of Earth, the Moon and the Sun.

A minimoon would remain captured by Earth until one of those tugs breaks the pull of Earth's gravity, and the Sun once again takes control of the object's trajectory.

While the typical minimoon would orbit Earth for about nine months, some of them could orbit our planet for decades.

This was one of the largest and longest computations I've ever done," said Vaubaillon. "If you were to try to do this on your home computer, it would take about six years."

In 2006, the University of Arizona's Catalina Sky Survey discovered a minimoon about the size of a car.

Known by the unimaginative designation 2006 RH120, it orbited Earth for less than a year after its discovery, then resumed orbiting the Sun.

Hot Jupiters: Stars that steal give birth to backwards planets

Stealing gas from their siblings could leave stars with a motley crew of planets – including ones with backwards orbits.

Our solar system is thought to have formed from a collapsing cloud of gas and dust that flattened out as it spun, rather like pizza dough. 

This explains why the planets all orbit the sun in the same direction as the sun itself spins, and share the same plane.

Exoplanets tell a different story, with some tilted at jaunty angles and others orbiting their stars backwards. Planet-on-planet violence is one explanation, but Ingo Thies of the University of Bonn in Germany and colleagues suggest the culprit is the star itself, before its planets are born.

The team made a computer model of stars forming in a cluster. The stars started out forming proto-planetary discs in the usual way. But if a star veered too close to another clump of matter, like another star's disc or a cloud of gas that hadn't formed a star yet, it sucked huge streams of gas – up to 30 times the mass of Jupiter – from its neighbours and into its own nascent disc.

Hot Jupiters

In the model, this stolen material tilted the disc. And when the angle and the mass of material were just right, the final disc ended up spinning in the opposite direction to the star. Any planets that formed in that disc did the same. The work will appear in Monthly Notices of the Royal Astronomical Society.

The influx of gas could also compress the inner part of the disc, making planets form there more quickly. These may be more susceptible to violent crashes, leading to further eccentric orbits.

This in turn could help explain why, unlike our solar system, which keeps the smallest and rockiest planets closest to the sun, many exoplanet systems have bloated gas giants, known as "hot Jupiters", as their innermost planets. When the smaller planets get flung out of the inner part of the disc, an overall conservation of angular momentum means these gas giants could get drawn in closer.

Reference: arxiv.org/abs/1107.2113

New Horizons Web Site

The computer-generated images below are simulated views of New Horizons' location in the solar system.

The images were created using the Satellite Tool Kit (STK) software, which was developed by Analytical Graphics, Inc. Images are updated every hour.

Click here to follow New Horizons as it passes each planet's orbit, starting with our own Moon.


This image shows New Horizons' current position.

The green segment of the line shows where New Horizons has traveled since launch; the red indicates the spacecraft's path toward Jupiter, Pluto and beyond.

Positions of stars with magnitude 12 or brighter are shown from this perspective, which is above the Sun and "north" of Earth's orbit.

For more information follow this link New Horizons Web Site

Milky Way has a huge hidden neighbour: A Large Perturber

A LARGE satellite galaxy may be lurking, hidden from view, next door to our own.

Sukanya Chakrabarti and Leo Blitz of the University of California, Berkeley, suspected that the gravity of a nearby galaxy was causing perturbations that have been observed in gas on the fringes of the Milky Way.

"We did a large range of simulations where we varied the mass of the perturber and the distance of closest approach," says Chakrabarti. In the best-fitting simulation, the unseen galaxy has about 1 per cent of the Milky Way's mass, or 10 billion times the mass of the sun.

That's a lot. It means the object has roughly the same mass as the Milky Way's brightest satellite galaxy, the Large Magellanic Cloud (LMC).

Right now, says Chakrabarti, the galaxy is roughly 300,000 light years away from us - about twice as far away as the LMC. But the simulations suggest it follows a highly elongated elliptical path, and about 300 million years ago it swept through our own galaxy just 16,000 light years from the galactic centre - closer in than Earth - disturbing the Milky Way's outskirts as it went.

"Overall, it is a very plausible scenario," says Abraham Loeb at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who was not part of the study. "Of course, the fact that we don't see such a massive satellite is an issue."

Chakrabarti suggests that the galaxy has remained hidden because it is not a brilliant spectacle. Whereas the LMC glistens with bright young stars and the gas that spawned them, the unseen galaxy may be dead, containing old stars and little gas.

To make matters worse, the simulations suggest that the galaxy orbits ours in the same plane as our galaxy's disc. If it is now on the opposite side of the galaxy from us, it could be hiding behind the thick gas and dust in the galactic plane. "It's very likely to be in a region of very high obscuration," says Chakrabarti. The work will appear in Monthly Notices of the Royal Astronomical Society.

By further studying the distribution of gas, Chakrabarti hopes to pinpoint the galaxy's location so that astronomers will know where to look for it. This parallels the way astronomers in the 1840s discovered Neptune from irregularities in the motion of Uranus caused by gravitational tugs from the more distant planet. If the unseen galaxy exists, it will be the first nearby galaxy detected through its gravity rather than its starlight.

Welcome back Endeavour

Endeavour kicked up dust as it touches down on Runway 15 at NASA's Kennedy Space Center in Florida to complete the 16-day, 6.5-million mile journey on the STS-127 mission to the International Space Station.

Endeavour landed on orbit 248. Main gear touchdown was at 10:48:08 a.m. EDT. Nose gear touchdown was at 10:48:21 a.m. and wheels stop was at 10:49:13 a.m.

Endeavour delivered the Japanese Experiment Module's Exposed Facility and the Experiment Logistics Module-Exposed Section to the International Space Station (ISS).

The mission was the 29th flight to the station, the 23rd flight of Endeavour and the 127th in the Space Shuttle Program, as well as the 71st landing at Kennedy.

Image Credit: NASA/Kim Shiflett

Laser Propulsion: Wild Idea May Finally Shine

New laser propulsion experiments are throwing light on how to build future hypersonic aircraft and beam spacecraft into Earth orbit.

Indeed, a "Lightcraft revolution" could replace today's commercial jet travel. Passengers would be whisked from one side of the planet to the other in less than an hour - just enough time to get those impenetrable bags of peanuts open.

Furthermore, beamed energy propulsion can make flight to orbit easy, instead of tenuous and dangerous.

That's the belief of Leik Myrabo an aerospace engineering professor at Rensselaer Polytechnic Institute in Troy, NY. He's an expert in directed energy applications, aerospace systems, space prime power, and advanced propulsion.

For the past three decades, Myrabo's burning desire has been to create and demonstrate viable concepts for non-chemical propulsion of future flight vehicles through his research and company Lightcraft Technologies, Inc., of Bennington, Vt.

"Typically, a new propulsion technology takes 25 years to mature...to the point where you can actually field it. Well, that time is now," Myrabo told SPACE.com.

Real hardware...real physics

Space Debris Shield: Radar Station Network

(Image: European Space Agency / Rex Features)

Keeping an eye on the increasing amount of space debris is no easy task

A WORLDWIDE network of radar stations could tackle the ever-growing problem of space debris - the remains of old rockets and satellites that pose an increasing threat to spacecraft.

The US government is launching a competition, which will run until the end of 2010, to find the best way of tracking pieces of junk down to the size of a pool ball. Three aerospace companies - Northrop Grumman, Lockheed-Martin and Raytheon - have each been awarded $30 million by US Air Force Space Command to design a "space fence" that will constantly report the motion of all objects 5 centimetres wide and larger in medium and low-Earth orbits.

"It's basically going to be an electronic tripwire," says Rich Davis, Northrop's special projects director in Linthicum, Maryland. "It will give you the orbit angle and time of day that every satellite or piece of debris passes any point you choose." Once you know that, he says, it is easy to calculate potential collision risks.

It will give the orbit angle and time of day that every piece of debris passes any point in space you choose

The fence will be a significant improvement on the US's current system - the Air Force Space Surveillance System - which was built in 1961. This covers space above the continental US and can only resolve and track objects that are at least 50 centimetres across, using VHF signals in the megahertz range. To track smaller objects requires S-band radar, in the gigahertz range.

The contenders will have to work out how best to construct a global network of S-band radars that will allow them to continually feed data to the Joint Space Operations Center at Vandenberg Air Force Base in California. JSpOC will in turn make data that is not militarily sensitive publicly available on www.space-track.org.

ION Drive to Power Regular Journeys to MARS!

You can now see Neptune in the Night Sky

Then felt I like some watcher of the skies
When a new planet swims into his ken

Thus wrote John Keats, referring to William Herschel's discovery of the planet Uranus a few years before in 1781. Measurements of the position of Uranus soon showed that it was under the gravitational influence of another planet, farther out in the solar system.

Interplanetary Internet on board ISS

The International Space Station is now testing a new communications protocol that could form the backbone of a future interplanetary internet (Image: STS-119 Shuttle Crew/NASA)

The Universal Wide Web (UWW) or Interplanetary internet now has its first permanent node in space, aboard the International Space Station (ISS).

The new software will make sending data from space less like using the telephone, and more like using the web. In the modern era of the web and information on demand, teams still have to schedule times to send and receive data from space missions.

But the newly installed system aboard the ISS could one day allow data to flow between Earth, spacecraft, and astronauts automatically, creating what is being dubbed the "interplanetary internet".

It sure beats the dial-up and 386-processor based technology that normally manages the ISS comms.

Sarah Washington - Destination Moon

Hot Gas Giants go Through Phases

A SUPER-HOT planet 1500 light years away has been seen waxing and waning like the moon. The discovery hints that hot gas giants come in two varieties.

The phases of Corot 1b were detected by a team at Leiden Observatory in the Netherlands, who analysed changes in the amount of red light from the system. A small component of the light smoothly dims and brightens as the planet orbits. This is probably alternation between the dark of Corot 1b's relatively cool night side and the glow of its red-hot day side, which permanently faces its star and reaches a temperature of about 2400 kelvin (Nature, DOI: 10.1038/nature08045).

The stark temperature difference contrasts with previous observations of another gas planet, HD 189733b, using the Spitzer Space Telescope, which found a fairly even temperature around the planet of about 1000 kelvin.

The theory is that fierce winds carry solar heat around HD 189733b, whereas on Corot 1b, metal oxides appear to absorb heat high in the stratosphere and quickly re-radiate it before it can be spread around. "What we observe really fits into the idea that there are two different types of planet in this range", says Leiden team member Ignas Snellen.

Hubble (HST) upgraded and returned to orbit

The space shuttle Atlantis has released the Hubble Space Telescope back into space, after five days of back-to-back spacewalks to repair and upgrade the 19-year-old observatory (Image: NASA)

A spruced-up Hubble Space Telescope has been released back into space after five days of spacewalks to repair and upgrade the ageing observatory.

The space shuttle Atlantis will now make its way back to Earth, ending the $1.1 billion mission, which aimed to extend Hubble's life to at least 2014 and vastly improve its vision.

Six days after grabbing hold of the telescope with the shuttle's 15-metre-long robotic arm, astronaut Megan McArthur lifted the telescope from the shuttle's payload bay and placed it back in its own orbit at 1257 GMT.

Now, the 19-year-old telescope will undergo an intensive testing period, in which astronomers and engineers will calibrate and assess the health of the newly-installed and repaired instruments. NASA hopes Hubble science operations will reach "full stride" by September, Hubble programme manager Preston Burch told reporters on Monday.

Venus is disappearing now

Venus' southern hemisphere, as seen in the ultraviolet. Credit: ESA

In about three weeks, we will lose a brilliant luminary that has been so much a part of our evening sky since the end of last summer.

The planet Venus, which shone so high and bright in the western sky during February, is now moving steadily lower with each passing night; it has begun its plunge down toward the sunset, soon to make its most dramatic exit from the evening sky since 2001.

Currently Venus is setting just under three hours after the sun in a dark sky. You can't miss it. Simply go out just after sunset and look West.

By March 12, Venus will follow the sun by only about two hours and on March 21 by just an hour. And by March 25 it will lie only 9-degrees to the upper-right of the setting sun (your clenched fist measures roughly 10-degrees at arm's length) and follows it down by only about a half an hour.

Sweeping toward Earth

The reason for Venus' rapid fall toward the sun is that the planet will pass inferior conjunction on March 27. That means Venus, which orbits the sun well inside Earth's orbit, will be between us and the sun [Video].

China readies it military space station

The first public appearance of China's military space station concept. The space station design was unveiled on a live broadcast to celebrate the Chinese New Year. Credit: CCTV

China is aggressively accelerating the pace of its manned space program by developing a 17,000 lb. man-tended military space laboratory planned for launch by late 2010. The mission will coincide with a halt in U.S. manned flight with phase-out of the shuttle.

The project is being led by the General Armaments Department of the People's Liberation Army, and gives the Chinese two separate station development programs.

Shenzhou 8, the first mission to the outpost in early 2011 will be flown unmanned to test robotic docking systems. Subsequent missions will be manned to utilize the new pressurized module capabilities of the Tiangong outpost.

Importantly, China is openly acknowledging that the new Tiangong outpost will involve military space operations and technology development.

Also the fact it has been given a No. 1 numerical designation indicates that China may build more than one such military space laboratory in the coming years.

"The People's Liberation Army's General Armament Department aims to finish systems for the Tiangong-1 mission this year," says an official Chinese government statement on the new project. Work on a ground prototype is nearly finished.

Air-breathing planes: the spaceships of the future?

Getting to space has never been simple. A standing army of thousands is needed to launch the space shuttle, land it safely, and refurbish it so it is once again ready for flight.

And even the most basic space rockets require multiple stages, whose weight is mostly taken up by oxidisers needed to burn fuel. Rockets launch vertically to minimise the time they spend where Earth's gravity is strongest and shed stages to reduce their weight as they climb.

For decades, engineers have dreamed of a better way: a single-stage-to-orbit vehicle that would be lighter, cheaper, and easy to reuse. A fleet of these vehicles, supporters say, could be almost as easy to maintain as conventional jet planes, reducing the preparation time before each launch from months to days or even hours.

Since most of a rocket's weight is taken up by oxidiser, one logical approach is to save weight by developing an engine that can use oxygen from the atmosphere to burn fuel at least part of the way.

Are we getting any closer to this goal? Last week, the UK firm Reaction Engines announced they had received €1 million from the European Space Agency to develop three key parts for an air-breathing rocket engine. The firm hopes those components could one day help fulfill a decades-old plan to build a space plane called Skylon, which could take off and land on a runway like a conventional jet.

But Skylon isn't the only game in town. Take a look at air-breathing technology and what it could mean for the future of spaceflight.

How do air-breathing engines work?

The basic air-breathing engine uses inlets at the front of the vehicle to suck in air. What happens after that depends on the design.

One common engine is the ramjet, which uses the geometry of the engine to slow air down. But ramjets are only useful at relatively low speeds. At hypersonic speeds - above 5 times the speed of sound, or Mach 5 - the slowed air is too hot to be useful for combustion.

A popular solution to this problem is the scramjet, which does not slow air down very much, but instead quickly mixes the fast-flowing air with fuel together to create thrust. But scramjets are only useful above Mach 5, meaning another system, perhaps a conventional rocket, is needed to propel the plane to hypersonic speeds.

How fast can air-breathing engines travel?

The answer is not yet clear, since the technology has not undergone many tests. But at a certain speed, researchers believe air can't be mixed fast enough with fuel to combust it. That puts a limit on how fast air-breathing engines can go and suggests they will need to depend on rocket power to get that last boost into orbit.

Estimates for the speed limit of scramjets, for example, range from Mach 12 to Mach 20 (depending largely on the type of fuel used), says Mark Lewis, an aerospace engineer at the University of Maryland in College Park. That's still short of the Mach 25 or so needed to reach orbit and means scramjet flights would begin and end with a rocket phase.

What is Skylon's approach?

Skylon's proposed engine would use a heat exchanger to cool incoming air from 1000 °C at Mach 5 to less than -100 °C. Once cooled, the air is mixed with liquid hydrogen and burned.

Unlike scramjets, Skylon is designed to run in air-breathing mode directly from launch up to a speed of Mach 5.5. At an altitude of 26 kilometres, the engine would switch to conventional rocket power and use onboard oxygen to propel the plane into space.

"It's a pretty unique concept," says Mark Hempsell, director of future programmes at Reaction Engines. "I think at the moment it's the only realistic way to make aircraft vehicles that go into space."

The design should be sufficient to power a 43-tonne plane that can loft 12 tonnes of payload into low-Earth orbit, about half what the space shuttle can carry, the firm says.

How far along is the technology?

The most well-developed hypersonic air-breathing engines are small ones that are easily adapted to act as missile propulsion systems.

Two of the longest and fastest hypersonic air-breathing flights on record were made by NASA's X-43, a 5-metre-long scramjet-powered vehicle that accomplished two powered flights lasting roughly 10 seconds at Mach 7 and Mach 10 in 2004.

But that might change soon. Later in 2009, the US Air Force plans to begin test flights of a scramjet called the X-51. A B-52 bomber jet will be used to carry the vehicle to an altitude of 15 km, where it will be released and run for 4 to 5 minutes, accelerating to Mach 6.

Given the range of options, what's the best engine to use?

"As with all these things, the devil is in the details," says propulsion expert Aaron Auslander of NASA's Langley Research Center in Hampton, Virginia.

There may be multiple ways to get to orbit. Picking the best design requires a better understanding of how cost effective and reliable the vehicles will be, Auslander says.

"I think all approaches are on the table," Lewis said. Reaction Engines is "looking at one possible combination of engine system, and there's really a much broader range of options we need to explore before we know what to fly up to orbit," he adds.

Because scramjets might operate over the widest range of speeds, possibly up to Mach 20, Lewis says, they might be the most effective choice: "The farther you can go in the atmosphere, the greater the advantage will be."

But because scramjets would need a rocket to launch, and rockets accelerate too fast for tires, a scramjet plane would either have to launch vertically or on some sort of rail system, says Lewis.

NASA OCO satellite crashes and burns

Satellite failure clouds future of US climate science

The failure of NASA's Orbiting Carbon Observatory (OCO) is a loss to climate science, but that loss could be doubly compounded if engineers can't correct what went wrong in time for NASA's next climate satellite to fly later this year.

That satellite, known as the Glory mission, is currently set to launch in November, but it's now on hold pending the results of the OCO investigation. Whereas OCO was build to measure greenhouse gases, Glory is designed to study the effects of aerosols on clouds. This has been called the "missing link" of climate science, and it's information that is needed as soon as possible to refine global climate models.

It's well known that clouds reflect sunlight, which has a net effect of making the Earth cooler. It's also known that minute particles called aerosols often become the nuclei around which water droplets form in clouds. But what nobody understands is exactly how much humans are affecting the clouds with all the aerosols we generate through combustion, agriculture and other dust-raising activities.

So a delay in getting Glory off the ground means a delay in filling in this crucial piece of the climate puzzle. But wait - it gets worse.

One of the instruments on Glory is the "Total Irradiance Monitor" (TIM). Its job is to measure the total light output of the Sun to a degree of precision that is simply unachievable on the ground. This is important because sunlight is the key input into global climate and it drives the whole system. The fact that some climate sceptics still site changes in the Sun's energy output as responsible for climate change speaks to the fact that we don't have a good handle on what the Sun is likely to be doing long-term and more data are urgently needed.

Solar irradiance has been measured continuously from space for about the last 30 years. But during the 1980's coverage was insufficient and the calibration is not good between instruments that measured the Sun before and after this period. The deficit has led to disputes and to opposite conclusions about the long-term trend in solar irradiance.

Right now the best instrument for measuring solar irradiance is on the SORCE satellite, which was launched in 2003 and is now well past its nominal mission lifetime.

The TIM instrument on Glory is a descendant of this device and scientists involved with the mission say it's vital for the two instruments to observe the Sun together for at least six months to preserve the continuity of the 30-year solar record. If not, says TIM instrument scientist Greg Kopp of the University of Colorado, "it puts the whole record in jeopardy".

That would mean we might not be sure if the Sun is getting brighter, dimmer or staying the same in the coming decades, which is essential information for climate modelling and policy-making.

Glory will be launched on the same model of Taurus XL rocket that failed to place OCO into orbit today. The likely cause of the failure - a fairing that decided not to separate - has been established. What is not clear is whether this will require changes that could push back the launch of Glory into 2010 or beyond. Obviously scientists are hoping this will not be the case, and that any changes can be made in parallel with their own preparations for launch. On the other hand, another failure would be disastrous.

Aurora from Space

Auroras: What powers the greatest light show on Earth?
See New Scientist's gallery of auroras

A few times a day, a gigantic explosion shakes the Earth's magnetic shield, triggering a chain of events that lights up the polar skies with dazzling auroras. These explosions are substorms, and how they happen has long been a mystery. Until now, no one has been able to explain how they gather the energy to create such spectacular displays, or what happens to trigger them.

Now a flotilla of NASA satellites is finally providing answers. They could help us understand not only one of nature's greatest spectacles, but also help predict more serious space weather, which can endanger satellites and astronauts, and even scramble electrical systems on Earth.

The northern and southern lights have fascinated people throughout human history, and there has been no shortage of attempts to explain them. Galileo described these auroras as sunlight reflected in vapours rising from the Earth, while Descartes proposed reflections from ice crystals instead. In the late 1600s, Edmond Halley was the first to correctly link the aurora to the Earth's magnetic field, though it wasn't until the 1950s that scientists confirmed that the display is created when electrons are funnelled by magnetic fields into the upper atmosphere.

Auroras, substorms and more hazardous kinds of space weather all begin with the solar wind - a thin, hot gas of charged particles ejected from the sun, laced with magnetic fields and threaded with electric currents. This magnetic hurricane is blowing over the planet at 1.6 million kilometres per hour, but we don't feel so much as a breeze. That's because most of it is deflected by the Earth's magnetic field, which maintains a zone of relatively calm weather around the planet, called the magnetosphere. As the solar wind blows past the Earth, it pushes and stretches this protective shield out on the night side of the planet, like hair blown in the wind.

Despite this protection, the solar wind buffets and stirs up the magnetosphere, sending high-energy particles showering into the Earth's upper atmosphere. There they light up the gases like a neon tube, creating an aurora that appears as a slowly shifting curtain of green light as the charged particles smash into oxygen atoms. These "quiet auroral arcs" are usually quite faint. "People will often not realise there's an aurora. The sky will look a bit weird maybe, with a diffuse glow," says Eric Donovan of the University of Calgary, Alberta, who monitors the aurora borealis in Canada.

When a substorm rips through the magnetosphere, though, unleashing the energy of a few megatons of TNT, the effects are unmistakable. Magnetic fields whip through space, the electrical currents that circle the magnetosphere thrash wildly, and the aurora is transformed into a much brighter and more dynamic display that sweeps across the sky for 10 to 15 minutes. "It is not uncommon to get a hundred or thousandfold increase in brightness," says Donovan. The aurora also becomes more colourful, as high-energy electrons smash into molecules of the air, exciting red and green light from oxygen and blue from nitrogen.

During a substorm, it is not uncommon to get a hundred or thousandfold increase in brightness

It was already known that what makes the difference between subtle auroral arcs and the dazzling light shows caused by substorms is the direction of magnetic field in the solar wind. Most of the time the field aligns with that of the Earth, which allows the solar wind to flow uninterrupted around the planet. When the two fields point in opposite directions, though, they can become connected, and that loads the magnetosphere with the energy needed to create a substorm. It was not clear exactly how this happened, however.

Satellites such as the Geotail mission, led by the Japan Aerospace Exploration Agency, have helped tell part of the story. Since 1992, Geotail has ranged around the long tail of the Earth's magnetic field, studying its interaction with the solar wind. But a single spacecraft can only tell what's happening at one point; it can't get a big picture of the rapid and complex changes that shake the whole magnetosphere. "In the past, we only had 'pinprick' observations," says David Sibeck of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

To broaden this view, NASA launched a flotilla of satellites, collectively named THEMIS, in February 2007 to catch substorms as they happen. The five small spacecraft orbit the Earth like juggled balls, each following a different looping path, so when something interesting happens in the magnetosphere there's a good chance that they will be in a suitable arrangement to see it.

Three months after launch, THEMIS encountered the beginnings of a substorm. "We had five spacecraft lined up in a row perpendicular to the outer boundary of Earth's magnetic field, some just inside, some just outside," says Sibeck.

This position turned out to be the perfect spot to answer one of the mission's questions: how the solar wind pumps energy into the magnetosphere to power a substorm.

THEMIS's recordings revealed changes in the Earth's magnetic field as the solar wind connected with the magnetosphere. A bulge of twisted magnetic fields formed and slid along its boundary, towards the night side of the Earth. The team recognised this as a phenomenon called a flux rope, which some researchers had suggested would be linked to substorms.

Flux ropes connect the magnetic fields in the solar wind with those of the magnetosphere and the two become entwined, linking Earth's domain with that of the sun. This allows high-energy particles to stream in, loading the magnetosphere with pent-up energy (see diagram).

As the solar wind blows over the Earth, it pulls on its end of the flux rope, dragging the rope and its magnetic fields away from Earth's day side and out into the tail of the magnetosphere.

As more and more flux ropes form and are pulled into the tail, the day side of the Earth loses more and more of its magnetic field. That does not go on forever, of course. "It would completely deplete the day-side magnetic field", says Vassilis Angelopoulos of the University of California in Los Angeles, who heads the THEMIS mission. Earth's shield would disappear, leaving us exposed to carcinogenic cosmic rays. Over geological timescales, the atmosphere might even be stripped away by the solar wind.

Clearly, and luckily for us, that doesn't happen. Instead, after a few hours of building magnetic tension, a substorm strikes. Several things happen almost simultaneously: the tail snaps, hurling plasma towards the Earth, and the electric current that girdles the Earth is disrupted. But which of these triggers the substorm and the resulting aurora? To find out, the THEMIS researchers needed to know which happens first.

There are two competing theories. One school of thought has it that the impetus must come from the powerful electric current that flows around the magnetosphere about 60,000 kilometres up. The motion of magnetic fields drives this current, as in a dynamo, and it is known to be boosted when magnetic field is added to the tail. Does it get so strong that it becomes unstable and showers the atmosphere with high-energy electrons?

The other theory is that the trigger comes from the tail itself. As more magnetic field is added to it, the tail gets compressed tighter and tighter. Around the pinched core of the tail, these magnetic fields point in opposite directions, one running outwards from the north pole and the other running in towards the south pole. As these two field lines are stretched and squeezed by the solar wind, perhaps the two opposing fields spontaneously reconnect, cutting the tail in half and sparking a substorm (see diagram).

As luck would have it, on 26 February 2008, a substorm hit while the THEMIS flotilla was strung out on the night side of the Earth, straddling the region where the current would be disrupted and also where the tail would be expected to snap and reconnect. It was the perfect opportunity to settle the argument.

The first thing the satellites recorded was the tail of the magnetic field snapping off and reconnecting, suggesting that substorms do start with changes in this area. Case closed? Not quite. There was also a big surprise for the THEMIS team. Angelopoulos expected that the break in the tail would first destabilise the current encircling the planet, which in turn would spray electrons down to Earth to cause the aurora. Instead, the aurora began to intensify about a minute after reconnection in the tail, and, crucially, before the disruption of the ring current. "I was shocked," says Angelopoulos. "We never expected that within a minute you would see the aurora light up."

Not everyone is convinced that the team's findings, settle the matter, however. Indeed, Anthony Lui of Johns Hopkins University in Baltimore, Maryland, disputes the whole sequence of events. He thinks that Angelopoulos and his team have misinterpreted the THEMIS data and that reconnection in the tail happens later. "Then the sequence would be opposite to that stated in the Science article, implying that current disruption is the trigger of substorms instead," Lui says.

Although the THEMIS team have since recorded several more substorms, with the same results, Lui maintains that the spacecraft have never been in quite in the right positions to give definitive results. Angelopoulos has decided to alter their orbits to address this problem. Over the coming months, that may remove any remaining controversy about what sparks substorms and perhaps explain how their auroras appear so quickly.

The mission might also illuminate the link between substorms and full-blown geomagnetic storms, which can cause more than a pretty display. These storms are caused by violent outbursts from the sun and can play havoc with satellites, scramble GPS signals, endanger astronauts and even blow power lines on Earth. During a geomagnetic storm there are typically several substorms, but how the two are connected is unclear. So far during the mission, solar activity has been low, but it should increase over the coming year or so, giving THEMIS a chance to watch a much larger storm unfold.

Angelopoulos will be looking forward to it, and not just for the scientific opportunities. Perhaps surprisingly for someone who spends much of his time pondering substorms, Angelopoulos has seen very few with his own eyes. That is part of his motivation to understand them. "I want to go and watch them, so I'm working on predictive models," he says. "With a good model of how the trigger mechanism works, it should be possible to predict the onset of a substorm to within minutes, he says. "Then I can run outside."