Thursday, November 15, 2007

Planets Found Forming in the Pleiades Star Cluster

As you gaze up at the familiar Pleiades star cluster, here's something new you can think about. Planets recently collided around two of the stars in the cluster, kicking up vast clouds of dust. New worlds are being formed, and destroyed, right before our very eyes. At least, if you've got the help from some of the most powerful telescopes on Earth, and in space.

This announcement was made by a team of astronomers using the Gemini Observatory in Hawaii and the Spitzer Space Telescope. Their findings will be published in an upcoming issue of the Astrophysical Journal.

The Pleiades star cluster - located in the constellation Taurus - is one of the most famous objects in the night sky. Easily visible to the unaided eye, it's even more spectacular in binoculars or a small telescope. Although it's often referred to as the "seven sisters", the cluster actually contains 1,400 stars, in various stages of formation.

One of the stars, known as HD 23514, has a little more mass than our Sun. The astronomers discovered that it's surrounded by an enormous disk of hot dust particles. Astronomers think that this is the debris from a planetary collision.

It's believed that these dust particles, the building blocks of planets, accumulate into comets and asteroid-size bodies and then clump together into larger and larger objects. This is a violent process, though. Some objects get bigger, and others collide, shattering into dust that astronomers can detect.

Astronomers think that this is a similar process that led to the formation of the Earth's moon. At some point in the early Solar System, a Mars-sized object collided with the Earth. The debris from that collision became the Earth and the Moon.

Two stars in the Pleiades cluster, HD 23514 and BD +20 307, are thought to be in this stage of evolution. They're between 100 and 400 million years old. Much younger stars can have this dust when they're 10 million years old, but it's usually dissipated by the time a star reaches 100 million years old. It takes enormous planetary collisions to get the dust spewing out again.

Hubble's View of Comet Holmes

Comet Holmes, which is now larger than the Sun. But don't get fooled. That beautiful image on the left was taken by amateur astronomer Alan Dyer from Alberta, Canada. Hubble's version on the right. It's not as pretty, but it's got inner bigness.

You already know the story. Comet Holmes was a boring comet out near the orbit of Jupiter when it flared up on October 23rd. The coma of gas and dust expanded away from the comet, and now it extends to a volume larger than the Sun.

Of course, astronomers scrambled to turn the mighty Hubble Space Telescope to join in on the sky show. The space observatory's Wide Field Planetary Camera 2 monitored the object for several days, capturing images on October 29, 31 and November 4.

The Hubble image reveals the comet's nucleus down to a resolution as small as 54 km (33 miles) across. The image was processed to reveal differences in dust distribution near the nucleus.

Astronomers found that there's twice as much dust along the east-west direction as the north-south direction. This gives the comet a bowtie appearance. Even 12 days after the outburst, when this picture was captured, the nucleus is still surrounded by bright dust.

This isn't the first time that Hubble has viewed Comet Holmes. Luckily, it actually captured an image back in June 15, 1999. Back then, there was no dust around the object, and Hubble couldn't reveal the nucleus. By measuring its brightness, astronomers estimated that Holmes is approximately 3.4 km (2.1 miles) across.

Once Holmes settles down again, astronomers will use Hubble to make another accurate measurement of its brightness. By calculating the difference, astronomers will be able to figure out how much mass it lost during this outburst.

Radical New Steering Thruster Tested

With the shuttle and station in the news these days, it's easy to forget there's a whole other space program in the works: Constellation. Over the next decade, we'll go back to the Moon - this time to stay. Although it's inspired by the Apollo program, each piece of hardware is being updated with the latest technology. This week a radical new type of engine was tested at Northrop Grumman; an engine that could help steer spacecraft in space.

Northrop Grumman, one of the contractors on the NASA Constellation Program, announced this week that they've tested a new rocket called the TR408.

First a little history. The original Apollo program used thrusters powered by fuels that could be stored at room temperature, but they weren't very powerful. Furthermore, they were made with toxic chemicals that could be a risk to astronauts and workers.

The new TR408 engine is a hybrid, which can run on almost any state of oxygen and methane. It could be all gas, for example, stored at room temperature. Or it could be all liquid, similar to the liquid oxygen/hydrogen that powers the space shuttle.

The engine was tested for more that 50 separate tests, and was able to generate a steady-state specific impulse of 340 seconds. Just to give you some context, the Apollo thrusters generated a specific impulse of 290 seconds. The shuttle's liquid hydrogen/oxygen engine gets about 450 seconds.

Although the TR408 doesn't match up to the efficiency of liquid hydrogen/oxygen, it looks like it'll be a great compromise for the unique requirements of space travel.

There are more advantages. The TR408 is a very simple design, consisting of only two propellant valves, and no other moving parts. Less moving parts, means less things that can break. They should also be relatively inexpensive to build.

Northrup Grumman was awarded the contract to develop the engine for NASA 16 months ago, and they're pleased with the progress so far.

Although this engine is designed for low thrust tasks, like steering a spacecraft, more powerful versions are in the works. NASA engineers recently tested a methane/liquid oxygen rocket for 103 seconds, and XCOR Aerospace is working on a version that was tested in a vacuum chamber.

Rosetta Flyby Shows the Earth's Night Side

Right on schedule on November 13th, ESA's Rosetta spacecraft made its 2nd earthly flyby; testing its scientific instruments, and receiving a much needed gravitational assist. About two hours before its flyby, the spacecraft captured this image of the Earth's night side, including Asia, Africa and Europe.

When it captured this image, Rosetta was about 80,000 km (50,000 miles) away from the Earth, above the Indian Ocean. It imaged the planet using its OSIRIS instrument.

You can make out the continents Asia, Africa and Europe by the lighted areas of population centres. With less electricity, Africa has large darkened regions. Australia is down at the lower right-hand side of the image, partly lit by the Sun.

Rosetta's closest approach occurred at 20:57 GMT (3:57 pm EST) at a height of 5,295 km (3,290 miles) above a region of the Pacific Ocean, just off the coast of Chile.

The spacecraft has now completed 3 billion km of its 7.1 billion km journey to reach comet 67/P Churyumov-Gerasimenko. This was the third planetary swing-by for Rosetta and its second swing-by of Earth.

Now on its way out, Rosetta will focus its instruments on the Moon, and the Earth/Moon system. You can expect more cool images, and maybe even one with both the Earth and the Moon in a single frame. Now that would put things into perspective.

Rosetta will be back. It's expected to make its third and finally flyby in November 2009. But not before it makes a visit to the asteroid belt, to study asteroid Steins in September 2008.