Mathematical crime-fighter helps hunt for alien worlds

A curious mathematical crime-fighter has just boosted our confidence that the galaxy is brimming with alien worlds.

The statistical phenomenon, called Benford's law, has been shown to fit existing data on both confirmed and candidate exoplanets. The results suggest that of the thousands of planetary candidates, the majority will turn out to be real worlds and not errors in the data.

Initially a mere mathematical oddity, Benford's law states that the first digits of the numbers in certain sets follow a pattern of probability. For the numbers in a variety of data sets, 1 is the leading digit about 30 per cent of the time. Higher digits are less frequent: on average, just 4.6 per cent of numbers in such sets begin with 9.

Thomas Hair at Florida Gulf Coast University in Fort Myers wondered if Benford's law would hold true even beyond the solar system. "I became intrigued with the idea that exoplanet mass might fit," he says.

Hair examined data from the online catalogue exoplanets.org, which lists 755 confirmed exoplanets and nearly 3500 planet candidates, many of them found only in the past few years by NASA's Kepler space telescope. Masses are given in multiples of Earth's or Jupiter's mass. He found that the figures closely fit Benford's law for both units.

"The close fit with Benford's law gives a confirmation to experts' belief that most of the candidates are valid," says Hair, who will present the work in January at the Joint Mathematics Meeting in Baltimore, Maryland.

Source: New Scientist

Comet? Asteroid? Hubble astronomers observe bizarre six-tailed space object

Astronomers using the NASA/ESA Hubble Space Telescope have observed a unique and baffling object in the asteroid belt that looks like a rotating lawn sprinkler or badminton shuttlecock. While this object is on an asteroid-like orbit, it looks like a comet, and is sending out tails of dust into space.

Normal asteroids appear as tiny points of light. But this asteroid, designated P/2013 P5, has six comet-like tails of dust radiating from it like the spokes on a wheel. It was first spotted in August of this year as an unusually fuzzy-looking object by astronomers using the Pan-STARRS 1 telescope in Hawaii.

Because nothing like this has ever been seen before, astronomers are scratching their heads to find an adequate explanation for its mysterious appearance.

The multiple tails were discovered in Hubble images taken on 10 September 2013. When Hubble returned

"We were literally dumbfounded when we saw it," said lead investigator David Jewitt of the University of California at Los Angeles, USA. "Even more amazingly, its tail structures change dramatically in just 13 days as it belches out dust. That also caught us by surprise. It's hard to believe we're looking at an asteroid."

One explanation for the odd appearance is that the asteroid's rotation rate increased to the point where its surface started flying apart, ejecting dust in episodic eruptions that started last spring. The team rules out an asteroid impact because a lot of dust would have been blasted into space all at once, whereas P5 has ejected dust intermittently over a period of at least five months.

Careful modelling by team member Jessica Agarwal of the Max Planck Institute for Solar System Research in Lindau, Germany, showed that the tails could have been formed by a series of impulsive dust-ejection events. Radiation pressure from the Sun smears out the dust into streamers. "Given our observations and modelling, we infer that P/2013 P5 might be losing dust as it rotates at high speed," says Agarwal. "The Sun then drags this dust into the distinct tails we're seeing."

The asteroid could possibly have been spun up to a high speed as pressure from the Sun's light exerted a torque on the body. If the asteroid's spin rate became fast enough, Jewitt said, the asteroid's weak gravity would no longer be able to hold it together. Dust might avalanche down towards the equator, and maybe shatter and fall off, eventually drifting into space to make a tail. So far, only a small fraction of the main mass, perhaps 100 to 1000 tonnes of dust, has been lost. The asteroid is thousands of times more massive, with a radius of up to 240 meters.

Follow-up observations may show whether the dust leaves the asteroid in the equatorial plane, which would be quite strong evidence for a rotational breakup. Astronomers will also try to measure the asteroid's true spin rate.

Jewitt's interpretation implies that rotational breakup may be a common phenomenon in the asteroid belt; it may even be the main way in which small asteroids "die". "In astronomy, where you find one, you eventually find a whole bunch more," Jewitt said. "This is just an amazing object to us, and almost certainly the first of many more to come."

The paper from Jewitt's team appears online in the 7 November issue of The Astrophysical Journal Letters.
to the asteroid on 23 September, its appearance had totally changed. It looked as if the entire structure had swung around.

Source: SpaceTelescope.org

Astronomers identify intergalactic gas station on the outskirts of the Milky Way

Our Galaxy may have been consuming clouds of gas in a magnetic wrapper to keep making stars for the past eight billion years.

That’s the conclusion of astronomers at CSIRO, Australia's national science agency.

Dr Alex Hill, the lead author of a study of the Smith Hydrogen Gas
Cloud, a large gas cloud falling into the our Galaxy from intergalactic space, explained:

“Clouds like this may provide the fuel for our Galaxy to make stars, but they must be held together by something, or they’d disintegrate when they hit the warm outer part of the Galaxy — the halo. They wouldn’t reach the Galaxy’s disk, where the star-making is going on.”

The investigators found that the Smith Cloud has a magnetic field. It’s 50 000 times weaker than the Earth’s, “but it’s probably still strong enough to keep the cloud together”, Dr Hill said.

The findings were published recently in The Astrophysical Journal.

“This is one of the few such clouds large enough for us to be able measure its magnetic field,” added Dr Naomi McClure-Griffiths, a member of the research team.

“It seems the cloud is protected by a magnetic bubble, the same way the Earth’s magnetic field protects it from the solar wind.”

Named after its discoverer, Gail Bieger (née Smith), the Smith Cloud is at least two million times the mass of our Sun. If it were visible to the naked eye, it would look 20 times wider than the full Moon.

The Smith Cloud is one of thousands of “high velocity clouds” of hydrogen gas flying around the outskirts of the Milky Way. Astronomers believe their origins are mixed, some stemming from burst “bubbles” in the gas of our Galaxy, some being primordial gas, and some associated with small galaxies our Galaxy’s gravity is shredding from a distance.

The Smith Cloud is probably either semi-primordial gas condensing from the halo of the Milky Way or gas stripped from another galaxy.

Traveling at around 80 miles a second (130 kilometers a second), the Smith Cloud is only 8 000 light-years from our Galaxy’s disk and will drive into it in less than 30 million years.Its impact should produce galactic fireworks of some sort – possibly a burst of star formation or a supershell of neutral hydrogen.

Related links:

An all-sky map of high-velocity clouds

Astronomy Picture of the Day: High Velocity Clouds and the Milky Wa