Tag: science

Fermi proves that novae produce gamma rays

12:56 pm

The Fermi Gamma-Ray Space Telescope has discovered that novae, small scale stellar explosions similar to some supernovae but far less powerful, also produce gamma rays when they explode.

A nova is a sudden, short-lived brightening of an otherwise inconspicuous star caused by a thermonuclear explosion on the surface of a white dwarf, a compact star not much larger than Earth. Each nova explosion releases up to 100,000 times the annual energy output of our sun. Prior to Fermi, no one suspected these outbursts were capable of producing high-energy gamma rays, emission with energy levels millions of times greater than visible light and usually associated with far more powerful cosmic blasts.

What is significant about this is that it demonstrates a solid link between novae and supernovae, since only recently have scientists shown that some supernovae also produce gamma ray bursts. It suggests that the two explosions are produced by somewhat similar processes, but at very different scales. This fact will have important ramifications in the study of stellar evolution and the death of stars. For example, some nova stars often go nova repeatedly. Other data suggest that some more powerful eruptions can be recurrent as well. Extending this recurrent pattern to supernova suggests many new theoretical possibilities.

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How the Earth gave the Moon a lemon shape

9:36 am

Scientists have found that the Earth’s gravity combined with the Moon’s rotation forced the satellite to become “lemon-shaped.”

As the Moon solidified, its rotation caused it to elongate along its polar axis. But because the length of the Moon’s rotation was the same as its orbit, with one hemisphere always facing the Earth, the tidal force of the Earth’s gravity then pulled at the center, distorting the Moon’s shape so that one hemisphere bulged Earthward.

This theory is not new, but these new calculations are more robust, lending greater weight to it.

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The early bombardment of the Earth

9:04 am

Using computer models based on the Moon’s crater record, scientists have developed a simulation of the great early bombardment of the Earth around 4 billion years ago.

The model suggests that the biggest asteroids to hit Earth would have been as large as 3,000 kilometres across. Between one and four would have been 1,000 kilometres wide or larger, it predicts, with a total of three to seven exceeding 500 kilometres in width. The most recent of these would have hit around 4.2–4.3 billion years ago.

In comparison with Earth’s mass, the amount of rock hitting the planet would have been tiny. But it would have had an enormous effect on Earth’s surface, says Marchi. A 10-kilometre-wide asteroid was enough to kill the dinosaurs, and studies4 show that one 500 kilometres across would vaporize all of the planet’s oceans. “At 1,000 kilometres, the effects would be so wide the planet would probably be completely resurfaced with material from the mantle,” he says.

More here, including animated gifs showing this bombardment unfold.

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ExoMars will likely miss 2018 launch date

9:06 am

Because of technical and financial issues the European/Russian ExoMars rover mission is expected to miss its 2018 launch window.

The main reason for the delay would be the ExoMars’ brand-new landing system, which is designed to safely take the rover through a fiery descent in the Martian atmosphere and then softly land it on the surface of the Red Planet.

In addition to its late development start, the landing system has a complicated share of responsibilities between Russia and Europe, which greatly slows down the work. For example, the overall landing system is being developed by NPO Lavochkin in Moscow, while its parachute system will be provided by Europe. Many other aspects of the mission are similarly intertwined.

To further complicate matters, NPO Lavochkin, which traditionally builds all Russian planetary probes, but also some of the highly classified military satellites, is notorious for its Soviet-style secrecy. As a result, it is harder for the two sides to coordinate the work, Europeans sources said. Finally, the translation of documents between Russian and English further delays the work on the project.

The program is also significantly over budget.

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The Milky Way shrinks

9:49 pm

The uncertainty of science: New research by astronomers suggests that the Milky Way is about half as massive as previously estimated.

In the sixties I remember astronomers claiming that the Milky Way was twice as big as Andromeda. Then it was considered half as big. Most recently it was considered about the same size. This new research makes it half as big as Andromeda again.

In other words, the data is very uncertain, and the scientists really don’t have a good handle on it. None of these conclusions should be taken very seriously. All we really know at this point is that the Milky Way and Andromeda are approximately comparable.

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ISEE-3 engine restart fails but the private effort continues

11:57 am

After numerous tries, the private effort to put ISEE-3 back into its original orbit has failed.

We have completely accomplished all of our original goals except for one: firing the ISEE-3 propulsion system in a sufficient fashion to alter its trajectory. We did operate the propulsion system briefly so as to correct the spin of the spacecraft, and to start the trajectory correction maneuver. The propulsion system works fine. The problem is that there is no longer any Nitrogen pressurant left in its tanks to allow it to work.

36 years and more than 30 billion miles have taken its toll on the spacecraft’s propulsion system. We have exhausted every option to bring the engines online so as to conduct the correction maneuver required to place it in its planned orbit. Without the pressurant it just won’t work.

Have they given up? No! Though the spacecraft will remain in a solar orbit where maintaining communications will be difficult if not impossible, they are going to try anyway, and are even going to run another crowd-sourcing campaign to finance it.

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Gaia commissioning complete

9:47 am

After several months of in-orbit analysis, engineers have declared the European space telescope Gaia ready to begin research.

There have been several issues that had raised concerns, but from the article it sounds as if the engineers have either corrected the problems or have found ways to overcome or mitigate them.

Gaia will measure the movement and location of a billion stars, allowing astronomers to map the Milky Way better than ever before.

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Messenger descends to Mercury

9:12 am

As Messenger continues its observations of Mercury engineers have now lowered its orbit to its closest approach yet, 62 miles.

They will lower the orbit even more in August and September, then raise it up again for its final few months of research at the innermost planet, after which the spacecraft will use its last fuel to impact the planet.

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Venus Express is alive

9:03 am

After diving into Venus’s atmosphere on an aerobraking test that could have destroyed the spacecraft, the European probe Venus Express has now successfully used its last bits of fuel to raise its orbit back to research height.

Its present orbit will probably decay sometime in December, when the spacecraft will burn up in the atmosphere. However, the scientists running the mission though that was likely to happen during the aerobraking maneuver. Instead, Venus Express is giving them about another half year of research.

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