Physical sciences news, 12/10/07-12/16/07

Milky Way

Stars occupying regions above and below the disk of a spiral galaxy like the Milky Way are said to be in the galaxy's halo. In our own galaxy it turns out that there are two distinct halo regions, and they are rotating in opposite directions.

• Milky Way's two stellar halos have opposing spins
• Discovery shows Milky Way halo is split in two
• Huge Newfound Part of Milky Way Rotates Backward

Extrasolar planets

Some other solar systems besides ours undoubtedly have rocky planets like Mercury which always show the same face to the host star. A computer simulation shows that there could be a narrow potentially habitable region between the light and dark sides of such a planet.

• 'Twilight zones' on scorched planets could support life

Gliese 581d

Gliese 581d is a rocky planet recently discovered in orbit around the red dwarf star Gliese 581. It has about 8 times the mass of Earth. Two teams have now done simulations of the atmosphere of Gliese 581d and concluded that an atmosphere could exist and have properties considered necessary for Earthlike life to develop.

• Gliese 581: one planet might indeed be habitable
• Gliese 581d: A Habitable World After All?
• Is Gliese 581 Habitable?
• More Evidence that Gliese 581 Has Planets in the Habitable Zone

Haze on HD 189733b

HD 189733b is a gas giant extrasolar planet of the yellow dwarf star HD 189733 A. Although previous observations had suggested the presence of water vapor in the atmosphere, the latest set observations using the Hubble Space Telescope did not find evidence of water, sodium, or potassium in the atmosphere. However, there was an indication that the atmosphere did contain a haze of dust particles of unknown composition about 1 micron in size.

• Hazy red sunset on extrasolar planet
• Dust in a Hot Jupiter's Atmosphere
• First Sunset Outside Our Solar System Glimpsed
• A Red Haze on Distant Exoplanet
• HD 189733b: A 'Murky' Extrasolar Planet

Silica and the possibility of life on Mars

One of NASA's Mars rovers has found what appears to be a a deposit consisting largely of silica (SiO₂) – very fine grained beach sand, essentially. On Earth such deposits are found only in certain hot springs or volcanic fumaroles. Here both such environments support a great deal of microbial life. If life ever existed on Mars, it would likewise probably have thrived in such an environment.

• Clues to a Steamy Martian Past
• Mars Rover Investigates Signs of Steamy Martian Past
• Mars robot unearths microbe clue
• Mars Rover Finding Suggests Once Habitable Environment
• Mars rover finds signs of microbial life
• Spirit's Big Discovery

Organic compounds on Martian meteorite ALH 84001

ALH 84001 is a meteorite whose composition indicates it crystallized from molten rock 4.5 billion years ago on Mars. Over 10 years ago a team of NASA scientists hypothesized that some very small (20-100 nm) structures in the meteorite might be traces of life, but the claim was quite controversial and is no longer widely accepted. However, a recent comparison of the meteorite with terrestrial rocks suggests that simple organic compounds found in ALH 84001 could have formed, as in their terrestrial counterparts, in a chemical process catalyzed by magnetite (Fe₃O₄).

• Building blocks of life formed on Mars
• Building Blocks of Life Formed on Early Mars?
• Life's Building Blocks Found in Mars Rock
• Allan Hills 84001 Analysis Confirms Building Blocks Of Life Also Formed On Mars
• Building Blocks of Life Can Form on Cold, Rocky Planets — Anywhere

Saturn's rings

When Saturn's rings were first examined close-up by the Voyager missions in the 1970s, it was concluded that they had formed relatively recently (like 100 million years ago) when a moon of Saturn was destroyed in a collision with another moon or an asteroid. But the latest evidence from the Cassini mission indicates that Saturn may have had similar rings since the formation of the solar system 4.5 billion years ago. However, it appears that material in the rings is continually accreting into new moonlets, only to be destroyed again in later collisions.

• Saturn's Rings May Be As Old As Solar System
• Saturn's rings 'may live forever'
• Saturn's Rings Older Than First Thought?
• Saturn's Rings Could Be as Old as the Solar System
• Saturn’s Rings More Ancient than First Thought
• Saturn's Rings: Moon Remnants Or As Old As The Solar System?

Greenhouse gases

A new study indicates that human destruction of peat bogs may be responsible for emission of amounts of CO₂ possibly 10% as much as all burning of fossil fuels. Another study proposes a new model, taking into account the role of nitrogen, of how carbon is recycled among plants, soils, and the atmosphere.

• Peatland destruction is releasing vast amounts of CO₂
• New model revises estimates of terrestrial carbon dioxide uptake

Arctic ice

Some scientists who have studied the melting of Arctic ice now believe the ice could melt entirely in summer as soon as 2013, instead of 2040 as previously thought. Even this summer the melting has resulted in sea surface temperatures, in some places, 5° C above average – a level never before recorded. And this summer's melt of the Greenland ice sheet was 10% more than the previous record from 2005.

• 'The Arctic is screaming' — summer sea ice could be gone in five years
• Arctic summers ice-free 'by 2013'
• Without its insulating ice cap, Arctic surface waters warm to as much as 5 C above average
• Greenland melt accelerating, according to CU-Boulder study

Near-record high temperatures

And overall, 2007 figures to be Earth's second-warmest year on record, while the past 10 years have been the warmest decade ever recorded.

• 2007 Brought Near-Record Heat
• 2007 data confirms warming trend
• 1998-2007 warmest decade, UN agency says at climate meet