Every once in a while, things align just right in the cosmos and make it rather easy to write these articles.

Last month, Mars was in the headlines because of its closest approach to Earth in its orbit as well as being in opposition, making the planet the biggest and brightest in the night sky in the past two years. This month, Mars is again in our sights because of a possible encounter with an asteroid, prompting speculation that the near pass may have a chance of hitting the Red Planet.

The asteroid, called 2007 WD5, passes within 30,000 miles of Mars on Jan. 29 at 11:55 p.m. HST. Scientists put the odds at 1 in 25 that the 160-foot diameter rock will smash into the planet. However, in astronomical terms, this is considered a near encounter because of uncertainties and unknown factors in the asteroid's orbit.

If such an event were to occur, the blast is estimated to release around three megatons of energy as it plows into the Martian ground at 3.4 miles per second. This would be similar to the Tunguska event in 1908, where an object exploded above the Earth in Siberia and demolished a forest area of 830 square miles.

Earth avoided a huge impact crater from the Tunguska explosion because our thicker atmosphere caused the meteor to disintegrate before it actually reached the surface. However, Mars has a much thinner atmosphere and if 2007 WD5 enters its atmosphere, it will impact the ground and create a half-mile wide crater and a huge plume of dust in the sky.

It would be incredibly interesting for scientists, who have not seen another planetary impact since the 1994 Shoemaker-Levy comet collision with Jupiter.

The interest would not only be academic. There is a growing awareness among scientists and administrators of the possibility and implications of an Earth impact.

There are thousands of Near Earth Objects orbiting our sun-comets and asteroids left over from the formation of the solar system 4.6 billion years ago. To date, more than 5,000 objects have been identified as NEOs, defined by how close they get to Earth at perihelion, the closest approach to the sun. A sub-group of NEOs are the PHAs, or Potentially Hazardous Asteroids, rocks greater than 500 feet in diameter approaching Earth at a distance of 4.6 million miles or less. To date there are 912 PHAs identified.

While 4.6 million miles between civilization and the fate of the dinosaurs may seem like a comfortable distance, it really isn't for astronomers. Earth doesn't orbit the sun alone and there are many factors that could influence and change the orbits of these objects. There are a few groups monitoring and searching the skies for NEOs, including one here in Hawai'i.

Pan-STARRS, the Panoramic Survey Telescope & Rapid Response System, is being developed at the UH Institute for Astronomy and is in prototype operation on Haleakala. When completed, four cameras, each with 1.4 billion pixels, will eventually scan the skies to track and detect potentially hazardous objects.

No one really knows how many objects out there have not been discovered. The estimated size for an object threatening life on a global scale is around 1.2 miles in diameter or larger. The object that ended the reign of the dinosaurs is thought to have been about 9.3 miles in diameter.

Obviously, asteroids or comets of that scale affect our planet in terms of millions of years, but there are many smaller but no less significant bodies that fall within the "major disaster" range.

So tracking and detecting NEO/PHAs is a good idea, but what happens once we discover one that is barreling toward us? There is no officially sanctioned plan by the U.S. or the world to react to such a threat. However, there are a couple of private foundations starting grassroots efforts. Former Hawai'i astronaut Ed Lu is part of one of those organizations, called the B612 Foundation.

Other organizations, including NASA, are supporting more studies of NEOs, not just for defensive purposes but also for the vast resources that these rocks contain. In addition, the asteroid field could be used as "stepping stones" to human exploration to Mars and beyond.

FIRST METEOR SHOWER OF THE YEAR

The Quadrantid meteor shower peaks on Thursday at 8 p.m. and the moon will not be in the way. The radiant will not rise until after midnight, however, so the best chances of seeing the shower is closer to the early morning hours rather than the start of the evening. The Quadrantids is one of the two really "good" meteor showers this year, the next one with the best conditions comes in April. New information for 2008 will be posted on our Web site shortly: www.bishopmuseum.org

THE PLANETS

Earth:

Reaches perihelion Wednesday, its closest point to the sun in its orbit, at 1:50 p.m. HST.

Mercury:

By the middle of January, Mercury starts to become visible in the west shortly after sunset but never reaches much height above the horizon. You will have to have a clear view of the west to see this little planet at all during the second half of the month. The inner planet will have a visitor — the Messenger spacecraft sent from NASA will approach its destination on Jan. 14 to execute the first of three fly-bys of Mercury before finally settling down in orbit (in 2011) to complete its mission of mapping the planet.

Venus:

Venus is rising a bit later now, at 4:30 a.m. at the beginning of January. By the second week of the month, the brightest planet is joined by the largest planet, as Venus and Jupiter prepare for a rendezvous in February. Look for the pair in the eastern dawn sky throughout the month.

Mars:

Mars spends the month high in the sky as darkness falls, between the horns of Taurus and the feet of Gemini. By the end of the month, it won't be as bright as it is at the start, because Earth is quickly speeding away from the Red Planet in its orbit. Look for a waxing moon close to Mars on Jan. 19.

Jupiter:

The giant planet has now moved into the morning sky and may be spotted just before sunrise in the east by the second half of January. Because the inner planet Venus moves faster, it appears to move closer to Jupiter as the month closes, and by the last few days of the month, the two brightest planets are a beautiful pair at dawn.

Saturn:

Saturn rises in the east a little after 10 p.m. in early January, then two hours earlier by the end of the month. The ringed planet is joined by a waning gibbous moon on the 23rd and 24th in the constellation Leo.

MOON PHASES

New Moon: Jan. 8

First Quarter: Jan. 15

Full Moon: Jan. 22

Third Quarter: Jan. 29

Reach Carolyn Kaichi at hokupaa@bishopmuseum.org or 847-8203.

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