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NASA Mars mission set for launch

A SPACECRAFT that will examine the upper atmosphere of Mars in unprecedented detail is undergoing final preparations for a scheduled launch at 5:28am Sydney time (1:28 p.m. EST Monday, Nov. 18 in the USA) from the Cape Canaveral Air Force Station in Florida.

NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission will examine specific processes on Mars that led to the loss of much of its atmosphere. Data and analysis could tell planetary scientists the history of climate change on the Red Planet and provide further information on the history of planetary habitability.

“The MAVEN mission is a significant step toward unravelling the planetary puzzle about Mars’ past and present environments,” said John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington. “The knowledge we gain will build on past and current missions examining Mars and will help inform future missions to send humans to Mars.”

Artist's concept of MAVEN

MAVEN (artist’s concept) will arrive at Mars in September 2014 to begin a detailed study of the planet’s atmosphere and its interaction with the solar wind. Image Credit: NASA Goddard Space Flight Centre.

2.5-tonne spacecraft will launch aboard a United Launch Alliance Atlas V 401 rocket on a 10-month journey to Mars. After arriving in September 2014, MAVEN will settle into its elliptical science orbit.

Over the course of its one-Earth-year primary mission, MAVEN will observe all of Mars’ latitudes. Orbital altitudes will range from 150 kilometres to more than 6,100 kilometres. During the primary mission, MAVEN will execute five deep dip manoeuvres, descending to an altitude of 125 kilometres, which marks the lower boundary of the planet’s upper atmosphere.

MAVEN will carry three instrument suites. The Particles and Fields Package contains six instruments to characterise the solar wind and the ionosphere of Mars. The Remote Sensing Package will determine global characteristics of the upper atmosphere and ionosphere. And the Neutral Gas and Ion Mass Spectrometer will measure the composition of Mars’ upper atmosphere.

More information: MAVEN mission

Adapted from information issued by NASA.

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Voyager sees solar wind run out of puff

Artist's impression of the heliosphere

Artist's impression of the bubble—the heliosphere—blown in interstellar space by the solar wind. The Voyager 1 spacecraft is soon to cross the boundary into interstellar space.

  • Voyager 1 launched on September 5, 1977
  • The most distant spacecraft from Earth – 17.4 billion km
  • Now exploring the boundary between Solar System and interstellar space

The 33-year-long odyssey of NASA’s Voyager 1 spacecraft has reached a new milestone…a distant point at the edge of our Solar System where there is no outward motion of solar wind.

The solar wind is a stream of hot ionised gas, or plasma, emanating directly outward from the Sun. It forms a bubble—known as the heliosphere—around our Solar System. The solar wind travels at supersonic speed until it crosses a shockwave called the termination shock. At this point, the wind dramatically slows down and heats up in the heliosheath.

Outside the bubble lies true interstellar space, through which blows a gentle “interstellar wind”.

Now hurtling toward that interstellar space some 17.4 billion kilometres from the Sun, Voyager 1 has crossed into an area where the solar wind speed has slowed to zero.

Scientists suspect the solar wind has been turned sideways by the pressure from the interstellar wind.

The event is a major landmark in Voyager 1’s passage through the heliosheath, the turbulent outer shell of the Sun’s sphere of influence, and the spacecraft’s upcoming departure from our Solar System.

Voyager spacecraft

The twin Voyager spacecraft were launched in 1977 to investigate the outer planets of the Solar System.

“The solar wind has turned the corner,” said Ed Stone, Voyager project scientist based at the California Institute of Technology. “Voyager 1 is getting close to interstellar space.”

Voyager shows us something new

Launched on September 5, 1977, Voyager 1 crossed a region called the termination shock in December 2004 into the heliosheath. Scientists have used data from Voyager 1’s Low-Energy Charged Particle Instrument to deduce the solar wind’s velocity.

When the speed of the charged particles hitting the outward face of Voyager 1 matched the spacecraft’s speed, researchers knew that the net outward speed of the solar wind was zero. This occurred in June, when Voyager 1 was about 17 billion kilometres from the Sun.

Because the velocities can fluctuate, scientists gathered four more monthly readings before they were convinced the solar wind’s outward speed actually had slowed to zero.

Analysis of the data shows the velocity of the solar wind has steadily slowed at a rate of about 72,400 kph each year since August 2007, when the solar wind was speeding outward at about 209,000 kph. The outward speed has remained at zero since June.

The results were presented at the American Geophysical Union meeting in San Francisco.

“When I realised that we were getting solid zeroes, I was amazed,” said Rob Decker, a Voyager Low-Energy Charged Particle Instrument co-investigator and senior staff scientist at the Johns Hopkins University Applied Physics Laboratory.

“Here was Voyager, a spacecraft that has been a workhorse for 33 years, showing us something completely new again.”

Entering a new frontier

Scientists think Voyager 1 has not crossed the heliosheath into interstellar space. Crossing into interstellar space would mean a sudden drop in the density of hot particles and an increase in the density of cold particles.

Researchers are putting the data into their models of the heliosphere’s structure and should be able to better estimate when Voyager 1 will reach interstellar space.

They currently estimate Voyager 1 will cross that frontier in about four years.

Diagram of Voyager and Pioneer spacecraft positions

Where are they now? Positions of the two Voyager spacecraft, and Pioneers 10 and 11. Voyager 1 (bottom right corner) is the most distant.

“In science, there is nothing like a reality check to shake things up, and Voyager 1 provided that with hard facts,” said Tom Krimigis, principal investigator on the Low-Energy Charged Particle Instrument, who is based at the Applied Physics Laboratory and the Academy of Athens, Greece.

“Once again, we face the predicament of redoing our models.”

A sister spacecraft, Voyager 2, was launched in August 20, 1977 and has reached a position 14.2 billion kilometres from the Sun.

Both spacecraft have been travelling along different trajectories and at different speeds. Voyager 1 is travelling faster, at a speed of about 61,100 kph, compared to Voyager 2’s velocity of 56,300 kph.

In the next few years, scientists expect Voyager 2 to encounter the same kind of phenomenon as Voyager 1.

The Voyagers were built by NASA’s Jet Propulsion Laboratory, which continues to operate both spacecraft.

Adapted from information issued by NASA / JPL.

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Saturn’s eerie polar light show

False-colour image of Saturn

This false-colour composite of 65 Cassini spacecraft images shows the glow of the aurora over Saturn's north polar region. The colours are: blue is sunlight reflecting from the rings and from one of Saturn's cloud levels; red shows where heat is coming from the interior of the planet; and green shows the aurora.

  • Mini-movie made of Saturn’s polar aurora
  • Uses data from NASA’s Cassini spacecraft
  • Aurora pulses in time with the Sun and Saturn’s spin

As if its rings weren’t spectacular enough, Saturn also puts on a light show for anyone who can see at the right wavelengths.

In this case, those eyes belong to NASA’s Cassini spacecraft, which has been orbiting the Ringed Planet since 2004.

Scientists using Cassini’s visual and infrared mapping spectrometer (VIMS) instrument have been studying Saturn’s aurora, the equivalent of Earth’s Northern and Southern Lights.

Aurorae occur when particles in the solar wind are directed along magnetic field lines towards a planet’s poles. Funnelling down into the atmosphere, they strike gas molecules and cause an eerie, but very pretty, glow.

“Cassini’s instruments have been imaging the aurora in magnificent detail, but to understand the overall nature of the auroral region we need to make a huge number of observations—which can be difficult because Cassini observation time is in high demand,” says Dr Tom Stallard of the University of Leicester in the UK.

Time-lapse video of Saturn's aurora

This time-lapse video covers 20 Earth hours—just under two whole Saturnian days. Parts of the aurora seem synchronised with the direction of the Sun (left-hand side), while other parts appear orchestrated with Saturn's magnetic field.

So Dr Stallard and his colleagues turned to other Cassini images that weren’t specifically targeted at the aurora—but which nevertheless happened to serendipitously capture it—to compile a short video that shows the aurora’s behaviour as Saturn rotates.

“Sometimes the aurora can be clearly seen, sometimes we have to add multiple images together to produce a signal,” Dr Stallard said.

The video shows the aurora changing considerably during the over the course of Saturn’s day, which is around 10 hours and 47 minutes in Earth time.

On the left-hand side of the video—the direction towards the Sun—the aurora brightens, indicating that it is being influenced by the Sun.

Other parts of the aurora seem more connected with the planet below; specifically, with the orientation of Saturn’s magnetic field as the planet spins.

“Saturn’s aurora are very complex and we are only just beginning to understand all the factors involved,” said Stallard.

Story by Jonathan Nally, editor

Images courtesy NASA / JPL / University of Leicester / University of Arizona.

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