Posts Tagged ‘solar system’

Incoming Cosmic Rays Hit Record High

19 Oct

The Earth was pummeled with record-setting levels of cosmic rays in 2009. Measurements from NASA’s Advanced Composition Explorer (ACE) and other spacecraft found that more high-energy particles from galactic space penetrated the inner solar system in the last few years than at any other time since the beginning of the space age.

The spike is almost certainly due to several weird aspects of the most recent solar minimum, and could be the start of a new normal for cosmic ray levels.

“It’s sort of like everything’s working in the same direction right now, to allow cosmic rays greater access to the inner solar system,” said space scientist Richard Mewaldt of Caltech. Mewaldt and colleagues published their findings Oct. 7 in Astrophysical Journal Letters.

Cosmic rays, high-energy particles that originate in the galaxy and smack into Earth from all directions at near-light speeds, can pose a danger to spacecraft and astronauts spending long periods of time outside the Earth’s protective magnetic field. Most of these particles, especially the less-energetic ones, are deflected by the solar wind, which blows a protective bubble around the solar system called the heliosphere.

This solar system shield fluctuates in effectiveness every 11 years, as the sun goes through its regular cycle from lots of sunspots and solar flares to relatively boring solar weather. When the sun is most active, the solar wind is strongest, and even fewer cosmic rays penetrate the barriers. At solar minimum, more cosmic rays make it through.

“Up until now they had been reaching a constant level each solar minimum,” Mewaldt said. “But this one was different. This cycle, they’re more intense than they were in the past.”

The most recent solar minimum started in 2006 and was expected to end in 2008, but the sun stayed quiet through 2010. Using data from the ACE spacecraft, which has been in orbit around the sun since 1997, and historical data from a series of short-lived spacecraft going back to 1965, Mewaldt and colleagues showed that the cosmic ray levels in 2009 were 20 to 26 percent greater than at any previous solar minimum.

There are three main reasons for the upswing in cosmic rays, Mewaldt said. The solar magnetic field has been weaker than usual, which means the magnetic field that permeates the solar system is weaker too, and less efficient at knocking cosmic rays aside.

The long years of low solar activity also contribute to the high cosmic ray numbers. The sun occasionally lets off enormous bursts of plasma called coronal mass ejections, which can block cosmic rays as they explode out into interplanetary space. But there were fewer of these bursts during the most recent solar minimum, and those that happened were smaller than usual. “That’s another thing that let down the barriers and let the cosmic rays come in easier,” Mewaldt said.

Finally, the constant stream of charged particles that makes up the solar wind is weaker, making the protective bubble of the heliosphere smaller and more permeable. Incoming cosmic rays have a shorter distance to go to reach the Earth, so wimpier particles that would normally never get here can now make the journey.

Astronomers have already seen the impact of these extra cosmic rays on spacecraft, which have shown a 25 percent increase in certain types of errors that result from cosmic ray strikes, Mewaldt says.

The increased cosmic rays could pose a bigger problem for astronauts heading to Mars or building a base on the moon.

“They’d feel the brunt of this radiation for a longer period,” Mewaldt said “It’s already a problem, this would just make it worse.”

Although cosmic ray levels started going back down in early 2010, Mewaldt thinks the new high could be part of the long-term pattern of the sun. Measurements of radioactive elements embedded in ice cores at the poles show that over the past 500 years, cosmic ray levels were 40 to 80 percent higher than in the early 1970s. That means the sun was quieter in the past than it has been in the last few decades.

“It could well be that we are going to one of these longer-term grand minima,” Mewaldt said. “We don’t know yet for sure if we’re starting into one of those periods, but it certainly looks possible. We’ll have to wait a little longer to say.”

“I believe that this paper is the first paper that really shows us how the heliosphere works as a big global system,” commented NASA astronomer William D. Pesnell. “I think it will become an important paper because of that.”

Image: NASA

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Planets Weighed Using Pulsar Flashes

23 Aug

The rotating corpses of massive stars can help scientists weigh the planets in the solar system. By carefully timing radio blips from spinning stellar leftovers called pulsars, astronomers have measured the masses of all the planets from Mercury to Saturn, plus all their moons and rings.

Until now, the only way to figure out the mass of a planet was to send a spacecraft past it. The spacecraft’s orbit is determined by the gravitational oomph of the planet (plus whatever moons lay within the spacecraft’s orbit), which in turn depends on the planet’s mass. The new method is the first to let astronomers weigh planets from the comfort of Earthbound observatories.

“That’s what’s remarkable about this technique,” said space technologist William Folkner of NASA’s Jet Propulsion Laboratory, a co-author of a study in the upcoming issue of Astrophysical Journal. “I can’t think of any other way to measure masses of planets from the Earth.” 

The new method relies on the clock-like regularity of a class of neutron stars called pulsars, the rapidly spinning remains of massive stars that died in supernova explosions. Pulsars shoot tight beams of radio waves into space that sweep across the sky like a lighthouse, so from Earth they appear to blink or pulse.

Because the Earth is always moving around the sun, the time it takes for these radio blips to reach us is always changing. To get rid of this effect, astronomers calculate when the pulse should reach the solar system’s center of mass, or barycenter — the point around which all the mass in the solar system moves. But because the planets’ arrangement around the sun is constantly changing, the barycenter moves around with respect to the sun, too.

To pin down the center of mass at a given time, astronomers use a special table of where all the planets are, called an ephemeris, plus values for the masses of the planets taken from previous space missions. If the masses are slightly wrong, then a regular, repeating pattern of timing errors appears in the pulsar data. For instance, if Jupiter’s mass is a bit off, then an error appears every twelve years, once for every time Jupiter orbits the sun. Correcting the value for Jupiter’s mass makes the error disappear.

“You can see that 12 year wiggle in timing of neutron stars,” Folkner said. “That tells you how far the sun is from the solar system barycenter, which tells you what the mass of Jupiter is.”

An international team of scientists used three different radio telescopes, the 1000-foot-wide Arecibo telescope in Puerto Rico, the 210-foot Parkes telescope in Australia and the 328-foot Effelsberg telescope in Germany to time the blips from four different pulsars over a period of 5 to 22 years. They then used computer models to use the pulsars’ times to calculate the masses of Mercury, Venus, Mars, Jupiter and Saturn.

The masses the team found are not as accurate as the best measurements from spacecraft flybys, but they’re close. The measurement for Jupiter, for instance, was found to be 0.0009547921 times the mass of the sun. This value is more accurate than the mass determined from the Pioneer and Voyager spacecraft, and less accurate than, but consistent with, the value from the later Galileo spacecraft, which includes more decimal places.

“Our error bars are larger than those of these spacecraft measurements,” said study co-author Andrea Lommen of Franklin & Marshall College. “We are admitting freely that you should still use the mass of Jupiter measured from the spacecraft, but it’s comforting to know that our measurement agrees with that.”

The new method is also the first that can measure the masses of everything in a planetary system, including moons and rings.

“Spacecraft flybys don’t tell us the mass of everything in the Jupiter system, only the parts inside the spacecraft orbit,” Folkner said. “With this pulsar timing mechanism, we’re sensitive to the entire system, including the moons that are outside the orbit of any spacecraft that have flown by.”

The technique is actually a stepping stone to studying something even more exotic: ripples in space-time called gravitational waves that were predicted by Einstein but have never been observed. The timing of pulsar blips should change slightly whenever a gravitational wave goes by, but in order to see these changes, astronomers have to subtract out all the other noise that could alter the pulsar’s clock.

This study is “a graphic demonstration that you really have to understand the solar system really well if you’re going to be able to confidently detect gravitational radiation,” commented astronomer Scott Tremaine of the Institute for Advanced Study in Princeton, New Jersey, who was not involved in the new work. “If they can continue to develop these techniques to the point where they can detect gravitational waves, that will be a dramatically important event.”

Image: The sun, Earth and Jupiter orbit a common center of mass. David Champion, MPIfR

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First Historic Image of Planet 3106 Trillion Miles From Earth [Telescopes]

18 Sep

Thanks to the distortion-reducing power of the ALTAIR adaptive optics system on the Gemini North telescope in Hawaii, three University of Toronto scientists were able to capture images of the star 1RXS J160929.1-210524 from a distance of about 500 light years away. The image is believed to be the first ever of a planet in an alien solar system around a sun-like star. The discovery is made even more significant because the "planet" lies a tremendous distance away from its parent star—challenging currently accepted theories about star and planet formation. It will take up to 2 years of research to determine whether or not this object is, in fact, tied to the star by gravity. [Gemini via ScienceNews via DVICE]

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