An asteroid gives Earth a close shave

An asteroid of a similar size to a rock that exploded above Siberia in 1908 with the force of a thousand atomic bombs whizzed close past Earth on Monday, astronomers said on 3rd March, 2009.

2009 DD45, estimated to be between 21 and 47 meters (68 and 152 feet) across, raced by at 1344 GMT on Monday, the Planetary Society and astronomers' blogs reported.

The gap was just 72,000 kilometers (44,750 miles), or a fifth of the distance between Earth and the Moon and only twice the height of satellites in geosynchronous orbit, the website space.com said.

The estimated size is similar to that of an asteroid or comet that exploded above Tunguska, Siberia, on June 30 1908, flattening 80 million trees in a swathe of more than 2,000 square kilometers (800 square miles).

2009 DD45 was spotted last Saturday by astronomers at the Siding Spring Survey in Australia, and was verified by the International Astronomical Union's Minor Planet Centre (MPC), which catalogues Solar System rocks.

The closest flyby listed by the MPC is 2004 FU162, a small asteroid about six meters (20 feet) across which came within about 6,500 kms (4,000 miles) of us in March 2004.

Comet Lunin comes closest to Earth

Stargazers are in for a treat as Comet Lulin will swing closest to Earth and is expected to be visible to the naked eye on Tuesday. Comet Lulin, also known as the "Green Comet" because of the green tint due the chemicals in its head, will be within 38 million miles from Earth.

"The comet is brightening every day as it approaches Earth," said Amar Sharma a Bangalore-based amateur astronomer who has been observing the comet for the past few days.

"On Tuesday, February 24 the comet will be at its closest approach to Earth and is expected to be visible to the naked eye," Nehru Planetarium Director N Rathnasree said.

The comet will be visible as a faint green smudge low in the east-southeast sky before dawn. If the weather is clear and there is no haze in the sky, one should be able to locate the comet. A pair of binoculars or a moderate telescope might be needed to view the comet from the light polluted areas of cities like Delhi, she added.

When it's able to be seen, the Comet Lulin will be just 61 million kilometres away — about 160 times the distance between the Earth and the moon — which will be its closest approach to our planet, according to NASA.

The comet, whose official name is C/2007 N3, is expected to appear about a third of the way up the southern sky, a few degrees from Saturn in the constellation Leo. It is called "Lulin" after Lulin Observatory in Taiwan, where astronomers discovered it last year.

Scientists are using NASA's Swift Satellite to track and study the comet as it approaches.

The satellite includes probes that detect ultraviolet and X-ray radiation, which can be used to learn more about its chemistry, said a news release Friday from the Science and Technology Facilities Council in the United Kingdom, which is collaborating with NASA.The satellite can detect hydroxyl molecules that are produced when water is broken down by ultraviolet light from the sun.

Possibility of continents and oceans on Venus

In a new research, scientists have claimed to detect evidence for granite highlands on Venus in data almost two decades old, which suggests that the planet may have once been far more like Earth, with oceans and continents.

According to a report in Nature News, the data includes nighttime infrared emissions coming from the surface of Venus, which was detected by NASA’s Galileo spacecraft in 1990.

Analyzing these data, an international team led by planetary scientist George Hashimoto, now at Okayama University, Japan, found that Venus’s highland regions emitted less infrared radiation than its lowlands.

One interpretation of this lower infrared emission from the highlands, according to the authors, is that they are composed largely of ‘felsic’ rocks, particularly granite. Granite, which on Earth is found in continental crust, requires water for its formation.

Dirk Schulze-Makuch, an astrobiologist at Washington State University in Pullman said: “This is the first direct evidence that early in the history of the Solar System, Venus was a habitable planet with plenty of water. The question is how long Venus remained habitable. But this gives new impetus for the search for microbial life in Venus’s lower atmosphere.

According to Kevin Baines, a scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, Before Galileo, researchers had believed that only radar could see through the dense clouds of sulphuric acid in Venus’s atmosphere to the surface. Detecting the surface in the infrared is a breakthrough.

The possible presence of granite also suggests that tectonic plate movement and continent formation may have occurred on Venus, as well as recycling of water and carbon between the planet’s mantle and atmosphere.

According to geophysicist Norm Sleep of Stanford University in California, the implication of continent formation is “quite significant”. Venus might have once been almost entirely underwater, although without further geochemical data, we don’t know whether this early ocean’s temperature was 30 degree Celsius or 150 degree Celsius.

Nowadays, the planet is a paragon of the uninhabitable, with an atmosphere of 96 percent carbon dioxide and a surface temperature of around 460 degrees C. Any life on Venus that hadn’t figured out how to colonize the cloud tops a billion years after the planet’s formation would have been in big trouble.

Venus moves closer to Sun

Planet Venus will now move closer to the Sun, making it appear brighter in the night sky.

Science Popularization Association of Communicators and Educators (SPACE) president Chander Bhushan Devgun said: “Venus was at its maximum elongation on Thursday on the day of Makar Sankranti, and now will move closer to the Sun”.

Elongation is an astronomical term which refers to the angle between the Sun and a planet as viewed from the Earth. When a planet is visible after sunset, it is near its greatest eastern elongation. When it is visible before sunrise, it is near its greatest western elongation.

The value of the greatest elongation for Venus is between 45 and 47. This value varies because the orbits of the planets are elliptical, rather than perfect circles. Also, the variation can be attributed to the inconsistency in orbital inclination. That is, each planet's orbit is in a slightly different plane. The silvery planet is "up" for more than three hours after sunset now-a-days.