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New explorations in the solar system.

Reductions in USA government spending have reduced NASA activity - but there are still many projects underway during 2011. Details of these projects are always interesting and provide useful contexts for the teaching of science in secondary schools. The following article provides up to date news about the continuing exploration of the solar system by NASA space probes and the Hubble Space Telescope. In particular, the article examines the latest discoveries on the asteroid Vesta, Pluto, Neptune, Titan and Jupiter.

NASA'S DAWN SPACECRAFT REACHES ASTEROID VESTA.

On July 17, 2011, NASA's Dawn spacecraft became the first probe ever to enter orbit around an object in the main asteroid belt between Mars and Jupiter.

Dawn will study the asteroid Vesta for a year before departing to meet the dwarf planet Ceres in July 2012. Observations will provide unprecedented data to help scientists understand the earliest chapter of our solar system. The data also will help pave the way for future human space missions.

Dawn took the image shown in Photo 1 during its current orbit of Vesta, travelling from the dayside to the night side. The large structure near the south pole that showed up so prominently in previous images is visible in the centre of the illuminated surface. Compared to other images, this one shows more of the surface beneath the spacecraft in the shadow of night. Vesta turns on its axis once every five hours and twenty minutes.

Dawn's study of the asteroid Vesta, marks a major scientific accomplishment and also points the way to the future destinations where people will travel in the coming years. President Obama has directed NASA to send astronauts to an asteroid by 2025, and Dawn is gathering crucial data that will inform that mission.

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The spacecraft relayed information to confirm it entered Vesta's orbit, but the precise time this milestone occurred is unknown at this time. The time of Dawn's capture depended on Vesta's mass and gravity, which only has been estimated until now. The asteroid's mass determines the strength of its gravitational pull. If Vesta is more massive, its gravity is stronger, meaning it pulled Dawn into orbit sooner. If the asteroid is less massive, its gravity is weaker and it would have taken the spacecraft longer to achieve orbit. With Dawn now in orbit, the NASA science team can take more accurate measurements of Vesta's gravity and gather more accurate timeline information.

For further information see: (http://down.ipLnoso.aov/)

NEW MOON AROUND PLUTO

The Hubble Space Telescope has discovered a new moon around Pluto. Previously known moons have the names Charon, Hydra and Nix. The new moon has the temporary name P4. Photo 2 shows P4 in two images taken about a week apart by Hubble. P4 is the smallest moon yet found around Pluto, with an estimated diameter of 13 to 34 km. By comparison, Pluto's largest moon Charon is 1,200 km across. Nix and Hydra are 32 to 113 km wide. The new moon lies between the orbits of Nix and Hydra, two satellites discovered by Hubble in 2005. P4 completes an orbit around Pluto roughly every thirty one days.

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The new moon was first seen in a photo taken with Hubble's Wide Field Camera 3 on June 28, 2011. The sighting was confirmed in follow-up Hubble observations taken July 3 and July 18. P4, Nix, and Hydra are so small and so faint, that scientists combined short and long exposures to create this image of Pluto and its entire moon system. The speckled background is camera 'noise' produced during the long exposures. The linear features are imaging artefacts. The Hubble observations will help NASA's New Horizons mission, scheduled to fly through the Pluto system in 2015.

For further information see: (http://science.noso.gov)

NEPTUNE COMPLETES ITS FIRST ORBIT AROUND THE SUN

During 2011, the planet Neptune completed its first orbit around the Sun since it was discovered in 1846. The Hubble Space telescope took images of Neptune to commemorate the event on June 25-26.

The Hubble images revealed high-altitude clouds in the northern and southern hemispheres. The clouds are composed of methane ice crystals. The absorption of red light by methane in Neptune's atmosphere gives the planet a distinctive aqua colour.

Neptune is the most distant major planet in our solar system. German astronomer Johann Galle discovered the planet on September 23, 1846. At the time, the discovery doubled the size of the known solar system. The planet is 4.5 billion kilometres from the Sun, thirty times farther than Earth. Under the Sun's weak pull at that distance, Neptune plods along in its huge orbit, slowly completing one revolution approximately every 165 years.

For further information and pictures of Neptune see: (http://nssdc.osfc.noso.oov/Dlonetorv/foctsheet/neptunefoct.html)

CASSINI At TITAN

The Cassini probe has been exploring the planet Saturn and its moons since 2004. Cassini has also been taking images of Titan, Saturn's largest moon.

Photo 3 shows a synthetic-aperture radar image of the surface of Titan taken by Cassini on June 21, 2011. The image covers an area 350 kilometres high by 930 kilometres wide, with resolution of about 350 meters per pixel. Three of Titan's major surface features - dunes, craters and the enigmatic Xanadu -- appear in this radar image. The hazy, bright area at the left that extends to the lower centre of the image marks the northwest edge of Xanadu, a continent-sized feature centred near the moon's equator. At upper right is the crater Ksa, first seen by Cassini in 2006. The dark lines running between these two features are linear dunes, similar to sand dunes on Earth in Egypt and Namibia.

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For further information see: (www.nasa.aov/cassfn/) and (http://saturn.ipLnaso.aov).

JUNO PROBE TO EXPLORE JUPITER

NASA's solar-powered Juno spacecraft, the centrepiece of a $1.1 billion mission to Jupiter, has been launched atop an Atlas 5 rocket on August 5, 2011 on a five-year voyage to the solar system's largest planet. Once in orbit around Jupiter's poles, Juno's instruments will precisely map the planet's gravitational and magnetic fields, probe its turbulent atmosphere and hidden interior, and study the mechanisms responsible for its powerhouse auroras, the strongest in the solar system.

Breaking into orbit around Jupiter in July 2016, Juno will swoop to within 5,000 km of the planet's cloud tops once each orbit to collect precise data about its magnetic and gravitational field strength. But it will do so in an orbit around the planet's poles, ducking below the intense radiation belts that concentrate high-energy, sub-atomic particles around the equator. The radiation belts at Jupiter are the most hazardous region in the entire solar system, other than going right to the sun itself. Even in a polar orbit, Juno will be exposed to the equivalent of 100 million dental X-rays over one year, according to a NASA mission overview. To survive the hellish environment, the spacecraft's electronics are housed in what amounts to a titanium vault. But exposure to even reduced levels of radiation will limit the spacecraft's useful life to about one year, or thirty three orbits. At that point, Juno will be ordered to crash into Jupiter's atmosphere, going out in a literal blaze of glory.

Built by Lockheed Martin Space Systems of Denver and managed by the Jet Propulsion Laboratory in Pasadena, Calif., Juno is the ninth spacecraft to study Jupiter and only the second to orbit the huge world. All of the earlier spacecraft were powered by radioisotope thermoelectric generators, or RTGs, which used thermocouples to convert the heat produced by radioactive decay into electricity. Juno is the first solar-powered spacecraft designed to operate at Jupiter's distance from the sun -- nearly 800 million kilometres -- where sunlight is twenty five times weaker than at Earth.

As a result, three huge solar panels were required, each one the size of a tractor-trailer, arranged starfish fashion around the central body of the spacecraft. At Earth's distance from the sun, the arrays would generate 14 kilowatts of power. At Jupiter's distance, they will provide just 400 watts to power Juno's science instruments and subsystems.

The Atlas 5 rocket that launched Juno, was not powerful enough to fling the spacecraft directly to Jupiter. Instead, Juno will fly past the orbit of Mars and then use on-board propulsion in September 2012 to drop back into the inner solar system for a velocity boosting Earth flyby on Oct. 12, 2013. That will give Juno the extra push it needs to reach Jupiter in July 2016.

Mission objectives include:

* Determining how much water may be in Jupiter's atmosphere, a key factor in theories about how the solar system first formed and the distribution of elements in the solar nebula.

* Measuring the composition, temperature and the motions of clouds deep in Jupiter's atmosphere.

* Characterization of the magnetic and gravitational fields to learn more about the interior structure of the planet and whether a solid core might be present.

* Studying Jupiter's magnetosphere and the intense auroras at the planet's poles to learn more about the planet's magnetosphere and its effects on the atmosphere.

* Determining the amount of oxygen in the atmosphere of Jupiter to provide a more refined sense of how much water ice contributed to the planet's formation.

Another key objective is to figure out whether Jupiter has a solid, rocky core of some sort under the crushing weight of the overlying atmosphere and a layer of metallic hydrogen that may exist in a region where pressures range from 2 million to 40 million times the atmospheric pressure at sea level on Earth.

Further information see: www.naso.gov fiuno/TS

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About the Author:

John Wilkinson is author of three astronomy books: Probing the New Solar System (CSIRO Publishing, 2009), The Moon in close-up (Springer, 2010), and New eyes on the Sun (Springer, 2011). Each book is available through on-line booksellers, bookshops or via the author's website (http://astroscimac.com).
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Title Annotation:Hands On
Author:Wilkinson, John
Publication:Teaching Science
Geographic Code:8AUST
Date:Dec 1, 2011
Words:1664
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