Transitional Regions at the Heliosphere's Outer Limits (

Voyager 1 Explores Final Frontier of Our ‘Solar Bubble’

Transitional Regions at the Heliosphere's Outer Limits (

Transitional Regions at the Heliosphere’s Outer Limits (

Data from Voyager 1, now more than 11 billion miles (18 billion kilometers) from the sun, suggest the spacecraft is closer to becoming the first human-made object to reach interstellar space.

Research using Voyager 1 data and published in the journal Science today provides new detail on the last region the spacecraft will cross before it leaves the heliosphere, or the bubble around our sun, and enters interstellar space. Three papers describe how Voyager 1’s entry into a region called the magnetic highway resulted in simultaneous observations of the highest rate so far of charged particles from outside heliosphere and the disappearance of charged particles from inside the heliosphere.

Scientists have seen two of the three signs of interstellar arrival they expected to see: charged particles disappearing as they zoom out along the solar magnetic field, and cosmic rays from far outside zooming in. Scientists have not yet seen the third sign, an abrupt change in the direction of the magnetic field, which would indicate the presence of the interstellar magnetic field.

“This strange, last region before interstellar space is coming into focus, thanks to Voyager 1, humankind’s most distant scout,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena. “If you looked at the cosmic ray and energetic particle data in isolation, you might think Voyager had reached interstellar space, but the team feels Voyager 1 has not yet gotten there because we are still within the domain of the sun’s magnetic field.”

Scientists do not know exactly how far Voyager 1 has to go to reach interstellar space. They estimate it could take several more months, or even years, to get there. The heliosphere extends at least 8 billion miles (13 billion kilometers) beyond all the planets in our solar system. It is dominated by the sun’s magnetic field and an ionized wind expanding outward from the sun. Outside the heliosphere, interstellar space is filled with matter from other stars and the magnetic field present in the nearby region of the Milky Way.

Voyager 1 and its twin spacecraft, Voyager 2, were launched in 1977. They toured Jupiter, Saturn, Uranus and Neptune before embarking on their interstellar mission in 1990. They now aim to leave the heliosphere. Measuring the size of the heliosphere is part of the Voyagers’ mission.

The Science papers focus on observations made from May to September 2012 by Voyager 1’s cosmic ray, low-energy charged particle and magnetometer instruments, with some additional charged particle data obtained through April of this year.

Voyager 2 is about 9 billion miles (15 billion kilometers) from the sun and still inside the heliosphere. Voyager 1 was about 11 billion miles (18 billion kilometers) from the sun Aug. 25 when it reached the magnetic highway, also known as the depletion region, and a connection to interstellar space. This region allows charged particles to travel into and out of the heliosphere along a smooth magnetic field line, instead of bouncing around in all directions as if trapped on local roads. For the first time in this region, scientists could detect low-energy cosmic rays that originate from dying stars.

“We saw a dramatic and rapid disappearance of the solar-originating particles. They decreased in intensity by more than 1,000 times, as if there was a huge vacuum pump at the entrance ramp onto the magnetic highway,” said Stamatios Krimigis, the low-energy charged particle instrument’s principal investigator at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “We have never witnessed such a decrease before, except when Voyager 1 exited the giant magnetosphere of Jupiter, some 34 years ago.”

Other charged particle behavior observed by Voyager 1 also indicates the spacecraft still is in a region of transition to the interstellar medium. While crossing into the new region, the charged particles originating from the heliosphere that decreased most quickly were those shooting straightest along solar magnetic field lines. Particles moving perpendicular to the magnetic field did not decrease as quickly. However, cosmic rays moving along the field lines in the magnetic highway region were somewhat more populous than those moving perpendicular to the field. In interstellar space, the direction of the moving charged particles is not expected to matter.

In the span of about 24 hours, the magnetic field originating from the sun also began piling up, like cars backed up on a freeway exit ramp. But scientists were able to quantify that the magnetic field barely changed direction — by no more than 2 degrees.

“A day made such a difference in this region with the magnetic field suddenly doubling and becoming extraordinarily smooth,” said Leonard Burlaga, the lead author of one of the papers, and based at NASA’s Goddard Space Flight Center in Greenbelt, Md. “But since there was no significant change in the magnetic field direction, we’re still observing the field lines originating at the sun.”

Artist's conception of a small icy object beyond Pluto (file picture).
Illustration courtesy G. Bacon, STScI/NASA

New Planet Found in Our Solar System?

Odd orbits of remote objects hint at unseen world, new calculations suggest.

Artist’s conception of a small icy object beyond Pluto (file picture).
Illustration courtesy G. Bacon, STScI/NASA

An as yet undiscovered planet might be orbiting at the dark fringes of the solar system, according to new research.

Too far out to be easily spotted by telescopes, the potential unseen planet appears to be making its presence felt by disturbing the orbits of so-called Kuiper belt objects, said Rodney Gomes, an astronomer at the National Observatory of Brazil in Rio de Janeiro.

Kuiper belt objects are small icy bodies—including some dwarf planets—that lie beyond the orbit of Neptune.

Once considered the ninth planet in our system, the dwarf planet Pluto, for example, is one of the largest Kuiper belt objects, at about 1,400 miles (2,300 kilometers) wide. Dozens of the other objects are hundreds of miles across, and more are being discovered every year….
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The Origin of the Solar System

Michael Perryman
This article relates two topics of central importance in modern astronomy – the discovery some fifteen years ago of the first planets around other stars (exoplanets), and the centuries-old problem of understanding the origin of our own solar system, with its planets, planetary satellites, asteroids, and comets. The surprising diversity of exoplanets, of which more than 500 have already been discovered, has required new models to explain their formation and evolution. In turn, these models explain, rather naturally, a number of important features of our own solar system, amongst them the masses and orbits of the terrestrial and gas giant planets, the presence and distribution of asteroids and comets, the origin and impact cratering of the Moon, and the existence of water on Earth…..
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What’s the weather like on other planets?

Anyone wanting to holiday on Mars should be prepared to take shelter from passing sandstorms Photo: AFP/GETTY IMAGES


he baby of the Solar system and closest to the Sun, smallest-planet Mercury has no atmosphere, so its weather forecast is usually fairly dull. However, visitors would be advised to either wrap up very warm, or slap on lots of SPF 50, depending on which part of the planet they stop off at – temperatures vary from -183C to 427C between the scorching subsolar point and freezing poles.


The hottest of all the planets, and second from the Sun, there’s no escaping the cloud cover on Venus. With an atmosphere that’s choked with carbon dioxide and nitrogen and suffused with sulphuric acid, glimpses of sunshine are unlikely. Mugginess doesn’t come close to describing the experience of sweating it out on the rocks with 92x the atmospheric pressure of Earth bearing down on you, trying to cool off in 480C heat.


The fourth planet from the Sun, Mars may have seen some heavy precipitation in the past but visitors these days would have to content themselves with strapping on their ice skates to explore the chilly polar regions. Expect to see blue sunsets and sunrises. Passing sandstorms on the horizon; take shelter.


Gigantic Jupiter is a gas planet, made up of hydrogen and helium. At 318 times the size of Earth, Jupiter gives off more heat than it gets from the Sun. Storms are highly likely as high pressure forces helium to become liquid, causing heavy rain, and winds of up to 360kph may be expected. Watch out for ammonia clouds, likely to be a common feature.


The sixth planet from the Sun, Saturn is also made up of gas. The second-largest planet in the Solar system is not a hospitable place, with winds of up to 1,800kph, temperatures up to 14,727C at the core and a layer of ice 10 kilometres thick. Cloudy days expected, made up of ammonia, hydrogen and helium. Every 30 years or so, a super-storm called the Great White Spot brews up. Saturn is best avoided at this time.


Stormy weather is forecast for this gas-and-ice planet, which is the third-largest and seventh from the Sun. Blue clouds of methane gas are expected, and visitors are advised to wear thermals to ward off the -197C chill.


Brrr. The blue planet – furthest from the Sun – is also aptly the coldest, with temperatures plummeting to -224C. Another gas giant but with an icy core, expect similar weather to Uranus but at the more extreme end. Winds can reach 2,100kph.

Extraterrestrial dust reveals asteroid’s past and future

The 500-metre-long Itokawa

Talk about seeing a world in a grain of sand. A sprinkling of asteroid dust that slipped into Japan’s Hayabusa probe when it touched down on the asteroid Itokawa six years ago has revealed surprising details about the space rock’s past and its likely future.

Hayabusa was meant to land on the 500-metre-wide asteroid in 2005 and fire projectiles into its surface, scooping up the resulting debris for later return to Earth. But the projectiles never fired, and team members had to wait five long years for the probe, which suffered numerous equipment failures, to limp back to EarthMovie Camera (see a picture of it after it touched down in Australia).

They hoped that some asteroid dust had managed to find its way into Hayabusa’s collection chamber when the probe touched Itokawa, but even when they saw dust there they were sceptical. “It was me who opened the sample catcher,” says Tomoki Nakamura of Tohoku University in Sendai. “I could not believe they were real Itokawa samples.”

Now, he and dozens of other researchers are reporting their analyses of the samples, which comprise more than 1500 rocky particles from Itokawa, all smaller than 0.2 millimetres across.

Larger parent

The studies suggest that Itokawa was once part of a much larger asteroid. The conclusion is based on the fact that the particles show a range of minerals that must have reached 800 °C to form (see picture). The decay of radioactive aluminium isotopes could have created that much heat if the parent body was at least 20 kilometres across – 40 times its current size, Nakamura and his collaborators say.

“The body needs to be big; otherwise, it would lose the temperature too quickly for these processes to occur,” says Trevor Ireland of the Australian National University in Canberra, who analysed some of the samples.

Indeed, data from Hayabusa itself had already determined that Itokawa has had its share of knocks in the past. The asteroid’s gravitational pull on the probe revealed that Itokawa has a very low density, suggesting it is a rocky rubble pile that probably coalesced after its parent body was smashed in an impact.

Dust that slipped into Japan's Hayabusa probe when it touched down on the asteroid Itokawa in 2005 pieces together its past and foretells its bleak future

Solar wind

The samples also hint at a bleak future for Itokawa. Keisuke Nagao of the University of Tokyo and colleagues studied noble gases, such as neon, in three grains. These gases can be implanted by charged particles streaming in from the solar wind and even from beyond the solar system.

The results suggest that the grains have been exposed to these charged particles for no more than 8 million years. This implies either that Itokawa coalesced 8 million years ago, or that it loses tens of centimetres of material from its surface every million years, exposing new layers of rubble in the process.

This could occur if dust grains lifted off the surface after micrometeoroid impacts simply float away from the lightweight asteroid. If Itokawa is losing its surface at that rate, it may completely disappear in less than a billion years.

Disappearing space rock

“It’s a bit sad to think it will eventually disappear,” says Scott Sandford of NASA’s Ames Research Center in California, who analysed some of the samples.

But he adds: “The ‘disappearance’ of Itokawa has its compensations. For one thing, I’d rather Itokawa be whittled away then to have it run into the Earth as a single object, which would cause some serious issues for the Earth if it happened. Also, one should remember that it is the process of whittling away at asteroids like Itokawa that produces the smaller meteoroids that ultimately land on the Earth as meteorites.”

This particular finding about its future may actually have been helped by Hayabusa’s failure to fire projectiles into the asteroid. “Solar wind penetrates only 100 nanometres or so into rock,” says Ireland. “The gun firing would have meant that the projectile penetrated into the asteroid, pushing out chips and fragments.” That would have made it “very hard to isolate surface pieces, which is where the solar wind resides”, he adds.

Link confirmed

The samples’ composition matches that of the most common type of meteorite found on Earth, called ordinary chondrites. Since Itokawa is classified as a stony S-type asteroid – the most common kind in the inner asteroid belt, the analyses confirm that ordinary chondrites come from S-type asteroids.

The studies also highlight the importance of returning samples from extraterrestrial bodies to Earth for study. “The analysis apparatus is too heavy to carry to an asteroid,” Nakamura told New Scientist.

Alexander Krot at the University of Hawaii at Manoa, who was not part of the team, says two other sample-return missions – Japan’s Hayabusa-2 and NASA’s OSIRIS-Rex – will blast off in 2014 and 2016 to collect samples from asteroids rich in minerals that formed in water.

These could reveal clues about “one of the most outstanding questions in planetary science – the origin of Earth’s water”, he says in a commentary in Science. Studies of hydrogen isotopes in the water-formed minerals in the target asteroids could help determine if Earth’s water was delivered by asteroids or comets or simply came from the dust from which the planet formed.

Journal reference: Science, DOI: 10.1126/science.1207758, 10.1126/science.1207776, 10.1126/science.1207865, 10.1126/science.1207794, 10.1126/science.1207807, 10.1126/science.1207785, 10.1126/science.1207758

Sun’s death rattle may hurl comets out of solar system

A DYING star deserves a last hurrah. It is fitting then, that our sun will throw many of its comets into interstellar space when it dies, according to new simulations.

In about 5 billion years, the sun will run out of hydrogen to burn in its core and will expand to become a red giant star. The red giant will blow off its atmosphere, leaving an ember-like core called a white dwarf.

It is generally accepted that planets inward of Earth and possibly Earth itself will be engulfed and incinerated during the red giant phase. But astronomers have paid little attention to more distant objects.

Now a study suggests that the sun’s death throes will reverberate all the way to the vast swarm of comets called the Oort cloud, out beyond Pluto.

When the sun loses mass, its gravity will decrease. This change can eject orbiting objects, but only if it happens on a timescale not much longer than the object’s orbital period. At the very end of the sun’s red giant phase, astronomers think it will shed a sizeable fraction of its mass in just 100,000 years or so.

This would still be too gradual to eject the planets beyond Earth, but simulations show that it will cause the exit of up to 20 per cent of Oort cloud comets into interstellar space, say Dimitri Veras and colleagues at the University of Cambridge. The work is to be published in Monthly Notices of the Royal Astronomical Society.

A Big Surprise from the Edge of the Solar System

NASA’s Voyager probes are truly going where no one has gone before. Gliding silently toward the stars, 9 billion miles from Earth, they are beaming back news from the most distant, unexplored reaches of the solar system.
Mission scientists say the probes have just sent back some very big news indeed.
It’s bubbly out there.

Magnetic bubbles at the edge of the solar system are aboout 100 million miles wide--similar to the distance between

According to computer models, the bubbles are large, about 100 million miles wide, so it would take the speedy probes weeks to cross just one of them. Voyager 1 entered the “foam-zone” around 2007, and Voyager 2 followed about a year later. At first researchers didn’t understand what the Voyagers were sensing–but now they have a good idea.
“The sun’s magnetic field extends all the way to the edge of the solar system,” explains Opher. “Because the sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina’s skirt. Far, far away from the sun, where the Voyagers are now, the folds of the skirt bunch up.”
When a magnetic field gets severely folded like this, interesting things can happen. Lines of magnetic force criss-cross, and “reconnect”. (Magnetic reconnection is the same energetic process underlying solar flares.) The crowded folds of the skirt reorganize themselves, sometimes explosively, into foamy magnetic bubbles.
“We never expected to find such a foam at the edge of the solar system, but there it is!” says Opher’s colleague, University of Maryland physicist Jim Drake.
Theories dating back to the 1950s had predicted a very different scenario: The distant magnetic field of the sun was supposed to curve around in relatively graceful arcs, eventually folding back to rejoin the sun. The actual bubbles appear to be self-contained and substantially disconnected from the broader solar magnetic field.
Energetic particle sensor readings suggest that the Voyagers are occasionally dipping in and out of the foam—so there might be regions where the old ideas still hold. But there is no question that old models alone cannot explain what the Voyagers have found.
Says Drake: “We are still trying to wrap our minds around the implications of these findings.”
The structure of the sun’s distant magnetic field—foam vs. no-foam—is of acute scientific importance because it defines how we interact with the rest of the galaxy. Researchers call the region where the Voyagers are now “the heliosheath.” It is essentially the border crossing between the Solar System and the rest of the Milky Way. Lots of things try to get across—interstellar clouds, knots of galactic magnetism, cosmic rays and so on. Will these intruders encounter a riot of bubbly magnetism (the new view) or graceful lines of magnetic force leading back to the sun (the old view)?

Old and new views of the heliosheath. Red and blue spirals are the gracefully curving magnetic field lines of orthodox models. New data from Voyager add a magnetic froth (inset) to the mix.

The case of cosmic rays is illustrative. Galactic cosmic rays are subatomic particles accelerated to near-light speed by distant black holes and supernova explosions. When these microscopic cannonballs try to enter the solar system, they have to fight through the sun’s magnetic field to reach the inner planets.
“The magnetic bubbles appear to be our first line of defense against cosmic rays,” points out Opher. “We haven’t figured out yet if this is a good thing or not.”
On one hand, the bubbles would seem to be a very porous shield, allowing many cosmic rays through the gaps. On the other hand, cosmic rays could get trapped inside the bubbles, which would make the froth a very good shield indeed.
So far, much of the evidence for the bubbles comes from the Voyager energetic particle and flow measurements. Proof can also be obtained from the Voyager magnetic field observations and some of this data is also very suggestive. However, because the magnetic field is so weak, the data takes much longer to analyze with the appropriate care. Thus, unraveling the magnetic signatures of bubbles in the Voyager data is ongoing.
“We’ll probably discover which is correct as the Voyagers proceed deeper into the froth and learn more about its organization,” says Opher. “This is just the beginning, and I predict more surprises ahead.”

Read also:
1. Voyagers ride ‘magnetic bubbles’
2. Voyager at the edge