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Dawn Closes in on Ceres

By David Reneke

A spacecraft is about to enter the orbit of Ceres, and construction of the world’s biggest optical and infrared telescope has been approved.

NASA’s Dawn spacecraft has commenced its approach to Ceres, a dwarf planet the size of NSW that has never been visited by a spacecraft. Dawn, launched in 2007, is scheduled to enter Ceres’ orbit on 6 March.

This is history in the making, for two reasons. Dawn’s arrival at Ceres will mark the first time that a spacecraft has ever orbited two solar system targets. Dawn previously explored the large asteroid Vesta in 2011, capturing detailed images and data about that body.

“Ceres is almost a complete mystery to us,” said Christopher Russell, principal investigator for the Dawn mission, based at the University of California, Los Angeles. “Ceres, unlike Vesta, has no meteorites linked to it to help reveal its secrets. All we can predict with confidence is that we will be surprised.”

The two planetary bodies are thought to be different in so many ways. Ceres may have formed later than Vesta, and have a cooler interior. Current evidence suggests that Vesta only retained a small amount of water because it formed earlier, when radio­active material was more abundant, which would have produced more heat. Ceres, in contrast, has a thick ice mantle and may even have an ocean beneath its icy crust.

Ceres, with an average diameter of 950 km, is the largest body in the asteroid belt between Mars and Jupiter. By comparison, Vesta has an average diameter of 525 km and is the second most massive body in the belt.

The spacecraft uses ion propulsion to cross space far more efficiently than chemical propulsion. In an ion propulsion engine, an electrical charge is applied to xenon gas, and charged metal grids accelerate the xenon particles out of the thruster. These particles push back on the thruster as they exit, creating a reaction force that propels the spacecraft.

Dawn has now completed 5 years of accumulated thrust time, far more than any other spacecraft. So, standby for transmission! The spacecraft’s images and other data will be the best ever taken of this enigmatic dwarf planet.

Green Light for the Biggest Eye on the Universe

The green light has been given for construction of the world’s biggest optical and infrared telescope, the European Extremely Large Telescope (E-ELT). The first phase of construction is currently underway, being built by the European Southern Observatory on top of Cerro Armazones in the Atacama Desert of northern Chile.

The E-ELT’s 39-metre diameter optical mirror, consisting of more than 600 hexagonal segments, will help unlock the mysteries of our universe, capturing 15 times more light than any other optical telescope currently in existence and creating images 16 times sharper than those produced by the Hubble Space Telescope.

A special correcting mirror in the telescope will be supported by more than 6000 actuators that can distort its shape 1000 times per second. The telescope’s main structure, when finished, will weigh about 2800 tonnes.

The E-ELT will search for extrasolar planets orbiting other stars. This will include not only the discovery of planets down to Earth-like masses through indirect measurements of the wobbling motion of stars perturbed by the planets that orbit them, but also the direct imaging of larger planets and possibly even the characterisation of their atmospheres.

Furthermore, the E-ELT’s suite of instruments will allow astronomers to probe the earliest stages of the formation of planetary systems and to detect water and organic molecules in proto-planetary discs around stars in the making. Who knows, we may finally understand the nature and distribution of dark matter and dark energy in the Universe.

When completed, this will be the world’s biggest eye on the sky. The E-ELT will answer fundamental questions regarding planet formation and evolution, and will bring us one step closer to answering the biggest question in human history – are we alone?

We’re entering the golden age of astronomy. The first phase of construction, at an approximate cost of €1 billion, will deliver a fully working telescope with a suite of powerful instruments. First light is targeted in 10 years.

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