Scientists: Plow the solar system through a dense-enough interstellar cloud and the heliosphere would no longer protect the Earth

The Earth's orbit outside the heliosphere

The uncertainty of science: Using a computer simulation, scientists have determined that if the solar system had two million years ago passed through one of the known nearby interstellar clouds within the relatively empty Local Bubble of space, it would have shrunk the Sun’s heliosphere enough so that the Earth would no longer be inside it, thus exposing the planet to interstellar space.

The image to the right comes from that simulation, and is figure 1 of the scientist’s paper [pdf]. The red line marks the Earth’s orbit (tilted sideways slightly to make it obvious), the yellow blob the shrunken heliosphere.

From the paper’s abstract:

There is overwhelming geological evidence from 60Fe and 244Pu isotopes that Earth was in direct contact with the ISM [interstellar medium] 2 million years ago, and the local ISM is home to several nearby cold clouds. Here we show, with a state-of the art simulation that incorporate all the current knowledge about the heliosphere that if the solar system passed through a cloud such as Local Leo Cold Cloud, then the heliosphere which protects the solar system from interstellar particles, must have shrunk to a scale smaller than the Earth’s orbit around the Sun (0.22).

Using a magnetohydrodynamic simulation that includes charge exchange between neutral atoms and ions, we show that during the heliosphere shrinkage, Earth was exposed to a neutral hydrogen density of up to 3000cm-3. This could have had drastic effects on Earth’s climate and potentially on human evolution at that time, as suggested by existing data.

This model is just one possible explanation of the presence of 60Fe and 244Pu isotopes on Earth. Another popular hypothesis is that a supernova occurred about 30 light years away, close enough to expose the Earth to interstellar space but not so close as to cause the total extinction of life.

With both theories, the event could also be an explanation for the significant climate changes two million years ago — such as the beginning of the most recent and now-ending ice age (no SUVs required) — as well as major evolutionary changes that occurred at that time among the ancestor species of humanity.

All is uncertain however. The scientists have no evidence the Earth actually entered a local dense cloud two million years ago. All they are doing is postulating that if such a thing happened, the dense cloud could shrink the heliosphere so much the Earth would be exposed to the interstellar medium.

Since we also do not yet have evidence of a specific nearby supernovae event either, neither theory can be favored. In fact, both could have been happened at different times in the past. Or neither.

Hat tip to reader Phil Berardelli, author of Phil’s Favorite 500: Loves of a Moviegoing Lifetime.

Interstellar space, as seen by both Voyager spacecraft

Today a suite of new science papers were published outlining what scientists learned when Voyager 2 joined Voyager 1 in interstellar space last November.

The Sun’s heliosphere is like a ship sailing through interstellar space. Both the heliosphere and interstellar space are filled with plasma, a gas that has had some of its atoms stripped of their electrons. The plasma inside the heliosphere is hot and sparse, while the plasma in interstellar space is colder and denser. The space between stars also contains cosmic rays, or particles accelerated by exploding stars. Voyager 1 discovered that the heliosphere protects Earth and the other planets from more than 70% of that radiation.

The data also shows that Voyager 2, which exited the heliosphere somewhat perpendicular to its direction of travel, is still in the transitional zone between the heliosphere and interstellar space. Voyager 1 exited out the head of the heliosphere, so its transitional zone was compressed and shorter.

The real achievement of these results however is that they were obtainable at all. For both spacecraft to be functioning so well after forty years in space, and able to get their data back to Earth from distances more than 11 billion miles, is a true testament to the grand engineering that went into their design and construction.

They built well in the mid-twentieth century.

Data from Voyager 2 suggests it is entering interstellar space

New data since August from Voyager 2 now suggests it is finally leaving the heliosphere of the solar system and entering interstellar space.

Since late August, the Cosmic Ray Subsystem instrument on Voyager 2 has measured about a 5 percent increase in the rate of cosmic rays hitting the spacecraft compared to early August. The probe’s Low-Energy Charged Particle instrument has detected a similar increase in higher-energy cosmic rays.

Cosmic rays are fast-moving particles that originate outside the solar system. Some of these cosmic rays are blocked by the heliosphere, so mission planners expect that Voyager 2 will measure an increase in the rate of cosmic rays as it approaches and crosses the boundary of the heliosphere.

In May 2012, Voyager 1 experienced an increase in the rate of cosmic rays similar to what Voyager 2 is now detecting. That was about three months before Voyager 1 crossed the heliopause and entered interstellar space.

The scientists warn that there is great uncertainty here, and that the actual transition into interstellar space might take longer than with Voyager 1 since Voyager 2 is traveling in a different direction and is leaving during a different time in the solar cycle.

Voyager 1 might not have left the solar system

The uncertainty of science: Two scientists dispute the finding this year that Voyager 1 has entered interstellar space.

Voyager has yet to detect what scientists long predicted would be the calling card of interstellar space: a shift in the direction of the magnetic field. Scientists had expected the probe to encounter particles under the influence of the interstellar magnetic field draped over the outer shell of the heliosphere, inducing an abrupt shift. But the direction has remained stubbornly constant, and researchers can’t explain why. “This whole region is a lot messier than anyone dreamed of,” Christian says.

It’s a bit too messy for George Gloeckler and Lennard Fisk, Voyager scientists at the University of Michigan in Ann Arbor. They wondered whether the magnetic field and particle density conditions measured by Voyager could exist within the heliosphere. In a paper accepted for publication in Geophysical Research Letters, Gloeckler and Fisk argue that the outer heliosphere could allow an influx of galactic particles from beyond the bubble that would explain the density measurements.

The researchers’ analysis includes a way to definitively test the idea: If Voyager 1 is within the heliosphere, Gloeckler and Fisk note, then it should still be at the mercy of the sun’s magnetic field. If that were the case, within a year or so, Voyager should detect a 180-degree flip in the field’s direction, a regular occurrence caused by the sun’s rotation. “If that happens,” Gloeckler says, “Len and I will have a big celebration.”

I suspect that both sides are right, and that the transition into interstellar space is simply very complex. Some data will say the spacecraft is outside the solar system, while other data will say it is inside.

Scientists today published a new model that suggests that Voyager 1 actually entered interstellar space in July of last year.

Ad astra: Scientists today published a new model that suggests that Voyager 1 actually left the solar system and entered interstellar space in July of last year.

In describing on a fine scale how magnetic field lines from the sun and magnetic field lines from interstellar space can connect to each other, they conclude Voyager 1 has been detecting the interstellar magnetic field since July 27, 2012. Their model would mean that the interstellar magnetic field direction is the same as that which originates from our sun.

Other models envision the interstellar magnetic field draped around our solar bubble and predict that the direction of the interstellar magnetic field is different from the solar magnetic field inside. By that interpretation, Voyager 1 would still be inside our solar bubble.

This new model might very well explain the conflicting data received from the spacecraft, some of which said it was out of the solar system and some of which said it was not.

Voyager 1 has found the edge of the solar system to be far more complex than predicted by scientists.

The uncertainty of science: Voyager 1 has found the edge of the solar system to be far more complex than predicted by scientists.

Scientists had assumed that Voyager 1, launched in 1977, would have exited the solar system by now. That would mean crossing the heliopause and leaving behind the vast bubble known as the heliosphere, which is characterized by particles flung by the sun and by a powerful magnetic field.

The scientists’ assumption turned out to be half-right. On Aug. 25, Voyager 1 saw a sharp drop-off in the solar particles, also known as the solar wind. At the same time, there was a spike in galactic particles coming from all points of the compass. But the sun’s magnetic field still registers, somewhat diminished, on the spacecraft’s magnetometer. So it’s still in the sun’s magnetic embrace, in a sense.

Voyager 1 at the edge

This week the American Geophysical Union (AGU) is having its annual fall meeting in San Francisco. Due to the wonders of technology, they are now making their press conferences available to reporters on line. Thus, I will be posting periodic updates after each conference. This will allow my readers to get a heads up on stories they will be seeing in the mainstream press in the next few hours.

Right now they are wrapping up a press conference from the team of the Voyager 1 spacecraft, in which they have described the spacecraft’s status.
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