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By David Reneke

A Plethora of Planets

Not many people are aware of it, but there’s an unofficial race going on among astronomers to find what’s been termed the “Holy Grail” of astronomy – a planet just like the Earth around another star. And they’ve come tantalisingly close. So close, in fact, that most are predicting we’ll find that world within the next 5 years!

Astronomers using the European Southern Observatory’s (ESO) world-leading exoplanet-hunting instrument HARPS recently announced a rich haul of more than 50 new exoplanets, including 16 so-called Super Earths, one of which orbits at the edge of the fabled “Goldilocks Zone” of its parent star. This is the zone astronomers believe could be hospitable to life because it is “not too hot or too cold”: a place where liquid water, and therefore life as we know it, could exist.

This is the largest number of such planets ever announced at one time, and shows that the pace of discovery is accelerating. But just because a planet is in the habitable zone doesn’t mean it has life. Mars is a good example of that.

The HARPS spectrograph on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile is the world’s most successful planet finder. “The harvest of discoveries from HARPS has exceeded all expectations,” said veteran planet-hunter Michel Mayor from the University of Geneva, Switzerland.

One of the recently announced planets, HD 85512 b, is estimated to be only 3.6 times the mass of the Earth and is located at the edge of the habitable zone. It’s not quite Earth-sized and ideally placed, but close.

In its 8-year history, HARPS has used the radial velocity, or “wobble”, method to discover more than 150 new exoplanets. When a large planet orbits a star it induces an axial wobble in one direction, then in the other as it completes one orbit.

HARPS is now so sensitive that it can detect changes in the rotation speed of a star, from dozens of light years away, of significantly less than 4 km/h! That’s less than walking speed.

With upgrades to both hardware and software systems in progress, HARPS is being pushed to the next level of stability and sensitivity to search for rocky planets that could support life. In the coming 10–20 years we should have the first list of potentially habitable planets in the Sun’s neighbourhood.

Dinosaur “Cold Case” Remains Unsolved
Chicken Little was right: the sky is falling. Or at least it was. Scientists have always been confident a 10–20 km-wide asteroid crashed into Earth around 65 million years ago, leading to the extinction of dinosaurs and some other life forms on our planet. The trouble is that no one knows for sure exactly where the asteroid came from, or how it made its way to Earth.

The only “evidence” we have points to a huge crater-shaped structure in the Gulf of Mexico and rare minerals in the fossil record that are common in meteorites but seldom found in the Earth’s crust.

However, observations from NASA’s Wide-field Infrared Survey Explorer (WISE) mission indicate that the family of asteroids believed to be responsible for the demise of the dinosaurs may not be the culprit, keeping the case open on one of the Earth’s greatest mysteries.

A 2007 ground-based telescopic study first pointed to the remnant of a huge asteroid known as Baptistina as a possible suspect. Formed from the collision with another asteroid in the main belt between Mars and Jupiter about 160 million years ago, it sent shattered pieces as big as mountains flying in all directions.

One of those pieces was believed to have impacted Earth, causing the dinosaurs’ extinction. But now new infrared observations from WISE show that Baptistina may not have been the responsible party after all. The “cold case” files are still open it seems.

WISE surveyed the entire asteroid belt, detecting infrared light related to a body’s temperature and size and, in some cases, age. The team measured the reflectivity and the size of 1056 members of the Baptistina family, and calculated that the original parent Baptistina asteroid actually broke up closer to 80 million years ago, half as long as originally proposed.

The results revealed that a chunk of the original Baptistina asteroid would need to have hit the Earth within 15 million years to cause the extinction of the dinosaurs.

"This doesn't give the remnants from the collision very much time to move into a resonance spot, and get flung down to Earth 65 million years ago. This process is thought to normally take many tens of millions of years," said study co-author Amy Mainzer of NASA's Jet Propulsion Laboratory.

So, the asteroid family that produced the dinosaur-killing asteroid remains at large. Next theory please!

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at www.davidreneke.com