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SHARON SHANKS | The Cosmos We're probing Mercury, but what about Pluto?



Published: Sun, June 24, 2001 @ 12:00 a.m.



From Mercury to Pluto, the astronomy & quot;in & quot; basket is simply overflowing with news. Let's do a little clearing out this week.

Mariner 10 was the last spacecraft to visit Mercury. It flew past three times and collected data on less than half the planet. Now, a generation later, a second visit is in the works. It's called MESSENGER, short for MErcury Surface Space ENvironment, GEochemistry, and Ranging, another triumph for NASA's famous acronyms.

Set for launch in March 2004 and arrival at Mercury in April 2009, MESSENGER will aim seven scientific instruments toward this closest planet to the sun.

A camera, a laser altimeter to measure the height of mountains and craters, and other instruments will be used to map the entire surface. Other devices will look at the composition of Mercury's crust, its geologic history, and the ingredients in its thin atmosphere.

MESSENGER will be a Discovery-class mission -- one of the quick to implement, relatively low-cost missions which NASA is supporting for solar system exploration. The mission's price tag comes in at $256 million.

Answers sought: Questions that scientists would like to answer about Mercury include why it is so dense (it has an extremely large core made mostly of iron) and how a planet so close to the sun -- averaging only 36 million miles away -- can have what appears to be ice in its polar craters.

At least Mercury has had one mission to date -- Pluto hasn't had any, and it appears the planet the farthest from the sun won't be visit by a spacecraft until 2020.

The Pluto-Kuiper Express was on the NASA drawing board, but it's not funded in the President's proposed NASA budget (effectively killing the project). The Planetary Society, one of the nation's largest private space interest groups, is hoping to change this -- and is taking its appeal to one of the most powerful lobbying groups in the nation: our children.

Kids to vote: & quot;Wouldn't it be cool to go to Pluto? & quot; is the challenge the society is putting before kids. Schoolchildren can log into a special Web page (http://planetary.org) to send their vote to Congress and get their legislators to change their minds.

Pluto averages 4 billion miles away from the sun. Even if Congress approves a mission this year, it couldn't be ready for launch until 2004 and the earliest it could reach Pluto would be 2012.

One mission that has been approved is targeting an even smaller body. Deep Impact is sent for launch in 2004. & quot;Deep Impact & quot; the movie envisioned an asteroid striking Earth; Deep Impact the mission will do just the opposite: launch a small instrument to impact Comet Temple 1.

By doing so, scientists will be able to study the pristine materials from inside the comet and hopefully learn more about our solar system.

Comet study: Comets, along with asteroids, planetesimals (bodies too small to be a planet but too large to be an asteroid), and meteors are some of the most primitive leftovers from the formation of the solar system.

By studying primordial material from within a comet, astronomers are hoping to learn what types and amounts of material were present when our star blazed into life.

A lot of items in the in-basket have the date June 21 on them. This past Thursday was a busy day: a total solar eclipse (visible from southern Africa), the summer solstice (the official start of summer and the longest day of the year), and, for people watching Mars, the date when the Red Planet makes its closest approach to Earth in the past 12 years.

You really can't miss Mars in the south. It will be the brightest starlike object in the southeast to south from dark until about 2 a.m. On Thursday Mars and Earth were only about 42 million miles apart.

The Mars Global Surveyor is still at work imaging Mars and recent photos have again focused on one of the most famous (or infamous) features there: the & quot;Face on Mars. & quot;

Viking 1 took the picture that started the fuss in 1976 and the hilly area did resemble a face -- just as clouds can resemble a dragon. The picture is now a standard in supermarket checkout publications, right beside pictures of Bigfoot, Area 51, little green aliens and the two-headed cows.

The newest image is in the highest resolution yet, and is best viewed online at Malin Space Science System's Web site. Malin designed and operates the Mars Orbiter Camera on the Global Surveyor.

XFor the Face on Mars, go directly to www.msss.com/mars_images/moc/extended_may2001/face/index.html.




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