Messenger Mercury: Collision With Giant Asteroid May Have Caused Spin Change

Updated NASA Messenger probe images obtained on September 29, 2011, shows a large crater with a floor partially covered by large numbers of Coalesced Hollows.

Mercury may have a lot in common with Earth, but close-up images and data captured by NASA'S MESSENGER probe this year show it's still a bit of a planetary weirdo. REUTERS/NASA/Handout

A new study suggests that Mercury's strange spin may have been caused by collision with a giant asteroid, which may have also caused Caloris Basin, Mercury's largest impact crater.

"Mercury once had a spin rate synchronous with the sun, like the moon with the Earth," said study co-author Alexandre Correia, a planetary scientist at the University of Aveiro in Portugal.

However, a giant asteroid may have collided with planet causing it to rotate three times on its axis for every two orbits it completes around the sun.

According to the study, computer models suggest that a giant impact from an asteroid knocked the planet it into its current strange configuration.

The space rock would have been at least 43 miles wide and 550 trillion metric tons in mass, or 1/600,000 the mass of Mercury, Correia said.

Evidence of the collision could include Mercury's largest impact crater, the Caloris Basin as it matches the predicted size, age and location of the impact.

Such an impact might also explain certain hollows seen on Mercury's surface, the researchers said.

Scientists had long assumed that Mercury was tidally locked with the sun, however, radar observations revealed that the planet led a far stranger life, rotating three times on its axis for every two orbits it completes around 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

ESA spacecraft performing well in orbit

The European Space Agency's Proba-2 spacecraft platform is in its second week in orbit and scientists say its operational health is excellent.

The mini-spacecraft and the ESA's SMOS satellite were launched aboard the same rocket Nov. 2 from the Plesetsk cosmodrome in northern Russia. Proba-2 is designed to demonstrate 17 advanced satellite technologies while observing the sun and the plasma environment in orbit, the space agency said.

The next step for Proba-2, which is expected to reach operational status within two months, is the commissioning of its many new technological payloads. The mini-satellite is among the smallest ever flown by ESA.

SMOS, ESA's full-sized Soil Moisture and Ocean Salinity spacecraft, will require more time to check and calibrate its equipment, the ESA said.

The Moon Belongs to the People of Earth, the Bold or no-one?

LAST week, NASA crashed its Lunar Crater Observation and Sensing Satellite (LCROSS) into the moon's south pole, in a bid to discover reserves of water and other resources.

This was the latest in a veritable flurry of moon missions: between 2007 and 2011 there will have been eight: one from Japan, two from China, one from India, one from Russia and three from the US.

The race back to the moon has been prompted by the realisation that exploiting it may now be within reach. And it poses the question: who gets to use the moon's recoverable resources, such as oxygen or water?

This could be resolved through negotiation, as space scientists happily lodging their instruments in foreign spacecraft hope. But the Lunar Treaty drafted by the United Nations in the 1990s has still not been signed by the space powers. Since this leaves the moon unprotected by law - the ultimate terra nullius - we may now see a scramble for territory.

The UN's Lunar Treaty is still unsigned by the space powers, leaving the moon unprotected by law
History shows that the first step is colonisation and - the pressing issue - staking a claim. Thanks to the explorers Amundsen, Scott and the early sealers, the UK and Norway now claim about one-sixth of Antarctica each. So we may be witnessing a slow-motion reworking of the Antarctica story in which lunar exploration lays the ground for claims.

We are already witnessing the same mix of challenge, bravado, inquiry and national enthusiasm, suffused with dreams of empire and wealth that spurred the Antarctic race. Plus, there's fear. "Whoever first conquers the moon will benefit first," as Ouyang Ziyuan, chief scientist of China's moon exploration programme, once told the BBC.

This potent cocktail can be used by scientists to win support for bigger, more aggressive national programmes. It is a long, expensive game but that never prevented it from being played out in the Antarctic for almost a century, and there are potential rewards to match.

When I put these ideas to David Parker, head of space science and exploration at the British National Space Centre, he called them Machiavellian. Perhaps he should recall that Machiavelli's Prince is the ultimate guide to realpolitik.

Appeal to Save the Mars Space flight Campaign: Give Generously

Humans could orbit Mars in the 2020s, says a panel appointed by the White House – but only if NASA's budget is boosted. At its current funding level, the agency will be unable to leave low-Earth orbit for at least the next two decades, according to a summary of the panel's report released on Tuesday.

Under President George W Bush, NASA was ordered to return astronauts to the moon by 2020. But in May, the Obama administration set up a panel of space experts to review the space agency's human spaceflight plans. The panel is led by former Lockheed Martin CEO Norman Augustine.

Though its final report is still being completed, on Tuesday the committee sent a summary of its findings to the White House and NASA. A final decision on NASA's future direction rests with the White House and Congress.

The summary contains a list of five possible ways forward for NASA's human spaceflight programme, without endorsing any particular one over the others.

One of those options, called the Flexible Path, would send astronauts to a series of increasingly distant destinations, starting with a mission to orbit the moon. A mission to an asteroid would follow later, and the plan would culminate in a mission to Mars, which the panel says could be achieved by the mid- to late-2020s.

To avoid breaking the bank, this option would delay development of any landing craft and other hardware needed to actually put astronauts on the planet's surface.

NEO: 3Km wide Asteroid in contra orbit - potential impact threat

The newly discovered asteroid 2009 HC82 travels on an orbit that is tilted by 155° with respect to the orbital plane of the planets, which means it travels in the opposite direction (Illustration: NASA/JPL)

The discovery of a 2- to 3-kilometre-wide asteroid in an orbit that goes backwards has set astronomers scratching their heads. It comes closer to Earth than any other object in a 'retrograde' orbit, and astronomers think they should have spotted it before.

The object, called 2009 HC82, was discovered by the Catalina Sky Survey in Arizona on the morning of 29 April.

From observations of its position by five different groups, Sonia Keys of the International Astronomical Union's Minor Planet Center calculated it orbits the sun every 3.39 years on a path that ventures within 3.5 million km of the Earth's orbit. Combined with its size, that makes 2009 HC82 a potentially hazardous asteroid.

HC82 a potentially hazardous asteroid.

What's really unusual is that the calculated orbit is inclined 155° to the plane of the Earth's orbit. That means that as it orbits the Sun, it actually travels backwards compared to the planets. It is only the 20^th asteroid known in a retrograde orbit, a very rare group. None of the others comes as close to the Earth.

The retrograde orbit of this asteroid will greatly increase the 'speed at impact' of this object, colliding with the Earth

The retrograde orbit of this asteroid will greatly increase the 'speed at impact' of this object and its potential for major damage. This is because both the Earth and HC82 will be travelling towards each other at high speed, like two trains heading towards each other on the same track.