Posted on by Jason Major

The Case of the Missing Dark Matter

Artist's impression of dark matter surrounding the Milky Way. (ESO/L. Calçada)

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A survey of the galactic region around our solar system by the European Southern Observatory (ESO) has turned up a surprising lack of dark matter, making its alleged existence even more of a mystery.

The 2.2m MPG-ESO telescope, used in the survey. (ESO/H.H.Heyer)

Dark matter is an invisible substance that is suspected to exist in large quantity around galaxies, lending mass but emitting no radiation. The only evidence for it comes from its gravitational effect on the material around it… up to now, dark matter itself has not been directly detected. Regardless, it has been estimated to make up 80% of all the mass in the Universe.

A team of astronomers at ESO’s La Silla Observatory in Chile has mapped the region around over 400 stars near the Sun, some of which were over 13,000 light-years distant. What they found was a quantity of material that coincided with what was observable: stars, gas, and dust… but no dark matter.

“The amount of mass that we derive matches very well with what we see — stars, dust and gas — in the region around the Sun,” said team leader Christian Moni Bidin of the Universidad de Concepción in Chile. “But this leaves no room for the extra material — dark matter — that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!”

Based on the team’s results, the dark matter halos thought to envelop galaxies would have to have “unusual” shapes — making their actual existence highly improbable.

Still, something is causing matter and radiation in the Universe to behave in a way that belies its visible mass. If it’s not dark matter, then what is it?

“Despite the new results, the Milky Way certainly rotates much faster than the visible matter alone can account for,” Bidin said. “So, if dark matter is not present where we expected it, a new solution for the missing mass problem must be found.

“Our results contradict the currently accepted models. The mystery of dark matter has just became even more mysterious.”

Read the release on the ESO site here.

Posted on by Jason Major

Cassini Slips Through Enceladus’ Spray

Cassini's latest view of Enceladus' icy spray, acquired on April 14, 2012.

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Spray it again, Enceladus! This Saturday the Cassini spacecraft paid another visit to Enceladus, Saturn’s 318-mile-wide moon that’s become famous for its icy geysers.During its latest close pass Cassini got a chance to “taste” Enceladus’ spray using its ion and neutral mass spectrometer, giving researchers more information on what sort of watery environment may be hiding under its frozen, wrinkled surface.

The image above shows a diagonal view of Enceladus as seen from the night side. (The moon’s south pole is aimed at a 45-degree angle to the upper right.) Only by imaging the moon backlit by the Sun can the geysers of fine, icy particles be so well seen.

During the flyby Cassini passed within 46 miles (74 km) of Enceladus’ surface.

This image was captured during the closest approach, revealing the distressed terrain of Enceladus’ south pole. Although a bit blurry due to the motion of the spacecraft, boulders can be made out resting along the tops of high , frozen ridges. (Edited from the original raw image to enhance detail.)

Enceladus' southern fissures, the source of its spray. (NASA/JPL/SSI/J. Major)

This flyby occurred less than three weeks after Cassini’s previous visit to Enceladus. Why pay so much attention to one little moon?

Basically, it’s the one place in our solar system that we know of where a world is spraying its “habitable zone” out into space for us to sample.

“More than 90 jets of all sizes near Enceladus’s south pole are spraying water vapor, icy particles, and organic compounds all over the place,” said Carolyn Porco, planetary scientist and Cassini Imaging science team leader, during a NASA interview in March. “Cassini has flown several times now through this spray and has tasted it. And we have found that aside from water and organic material, there is salt in the icy particles. The salinity is the same as that of Earth’s oceans.

“In the end, it’s the most promising place I know of for an astrobiology search,” said Porco. (Read the full interview here.)

A crescent-lit Enceladus sprays its "habitable zone" out into space.

Not to be left out, Tethys was also paid a visit by Cassini. The 662-mile-wide moon boasts one of the most extensively cratered surfaces in the Solar System, tied with its sister moons Rhea and Dione. In this raw image captured by Cassini on April 14, we can see some of the moon’s ancient, larger craters, including Melanthius with its enormous central peak.

Saturn's moon Tethys, imaged by Cassini on April 14, 2012.

Cassini passed Tethys at a distance of about 6,000 miles (9000 km) after departing Enceladus. Cassini’s composite infrared spectrometer looked for patterns in Tethys’ thermal signature while other instruments studied the moon’s geology.

Image credits: NASA/JPL/Space Science Institute. See more images from the Cassini mission on the CICLOPS site here.

 

Posted on by Jason Major

Hubble Reveals Curious Auroras on Uranus

Bright spots of Uranus' short-lived auroras have been imaged with the Hubble Space Telescope.

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Astronomers have finally succeeded in capturing the first Earth-based images of the curious and fleeting auroras of Uranus using the Hubble Space Telescope, careful planning… and no small amount of luck.

Unlike Earthly auroras, whose long-lived curtains of glowing green, red and purple have been the subject of countless stunning photos over the past months, Uranus’ auroras are relatively dim and short-lived, lasting only several minutes at most. They were first witnessed on Uranus by Voyager 2 in 1986, but never by any Earth-based telescopes until November of 2011. Using Hubble, an international team of astronomers led by Laurent Lamy from the Observatoire de Paris in Meudon, France spotted two instances of auroras on the distant planet… once on November 16 and again on the 29th.

Two instances of Uranian aurora imaged in Nov. 2011. (L. Lamy)

Auroras are known to be created by a planet’s magnetosphere, which on Earth is aligned closely with the rotational axis — which is why auroras are seen nearest the polar latitudes. But Uranus’ magnetic field is quite offset from its rotational axis, which in turn is tipped nearly 98 degrees relative to its orbital path. In other words, Uranus travels around the Sun rolling on its side! And with a 60-degree difference between its magnetic and rotational axis, nothing on Uranus seems to point quite where it should. This — along with its 2.5-billion-mile (4 billion km) distance — makes for a “very poorly known” magnetic field.

“This planet was only investigated in detail once, during the Voyager flyby, dating from 1986. Since then, we’ve had no opportunities to get new observations of this very unusual magnetosphere,” said Laurent Lamy, lead author of the team’s paper Earth-based detection of Uranus’ aurorae.

Rather than rings of bright emissions, as witnessed on Earth as well as Saturn and Jupiter, the Uranian auroras appeared as bright spots of activity on the planet’s daytime side — most likely a result of Uranus’ peculiar orientation, as well as its seasonal alignment.

It’s not yet known what may be happening on Uranus’ night side, which is out of view of Hubble.

When Voyager 2 passed by Uranus in 1986 the planet was tipped such that its rotational axis was aimed toward the Sun. This meant that its magnetic axis —  offset by 60 degrees — was angled enough to encounter the solar wind in much the same way that Earth’s does. This created nightside auroras similar to Earth’s that Voyager saw.

By 2011, however, Uranus — which has an 84-year-long orbit — was near equinox and as a result its magnetic axis was nearly perpendicular with its orbital plane, aiming each end directly into the solar wind once a day. This makes for very different kinds of auroras than what was seen by Voyager; in fact, there’s really nothing else like it that astronomers know of.

“This configuration is unique in the solar system,” said Lamy.

Further investigations of Uranus’ auroras and magnetic field can offer insight into the dynamics of Earth’s own magnetosphere and how it interacts with the solar wind, which in turn affects our increasingly technological society.

The team’s paper will be published Saturday in Geophysical Research Letters, a journal of the American Geophysical Union.

Read the release from the AGU here.

Posted on by Jason Major

Watch Mercury Get Smacked By CMEs

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The bright object in the center of this video sequence is the planet Mercury, seen by NASA’s STEREO-B spacecraft as it was pummeled by wave after wave of solar material ejected from the Sun during the week of March 25 – April 2, 2012.

The video above was released by NASA’s Goddard Space Flight Center earlier today. The Sun is located just off-frame to the left, while Earth would be millions of miles to the right.

Proof that it’s not easy being first rock from the Sun!

Video credit: NASA/GSFC/STEREO

Posted on by Jason Major

Ice Sculptures Fill The Deepest Parts of Mars

Credit: NASA/JPL/Arizona State University

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One of the “weirdest and least understood” areas of Mars, the enormous Hellas Impact Basin contains strange flowing landforms that bespeak of some specialized and large-scale geologic process having taken place. The HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter recently captured the image above, showing what’s being called “lava lamp terrain” — stretched and contorted surface that looks like overworked modeling clay or pulled taffy… or, with a bit of imagination, the melted, mesmerizing contents of a party light from another era.

At 1,400 miles (2,300 km) across, Mars’ Hellas Basin is one of the largest impact craters in the entire Solar System. Its vast interior sinks to a depth of about 23,000 feet (7152 meters) below Mars’ average surface elevation (Martian “sea level”, if you will) and thus its floor is often shrouded by haze and dust, making visual imaging difficult.

The “lava lamp” terrain is just one of many different types of landforms that are found in the basin, although many of these banded features are found in the northwest area — which is also the deepest part of the basin. If there had been water in the region at some point in the planet’s history, it would have concentrated there.

Although the texture at first appears as if it could be volcanic in origin, it’s thought that flowing water or ice may actually be the source.

Researchers are currently working to determine how the Hellas Basin became so smoothly sculpted. Nicolas Thomas, Professor of Experimental Physics at the University of Bern, Switzerland, told Universe Today:

“There are a lot of very interesting images from this area and we are trying to get more data (including stereo) to understand better what’s going on and to try to establish what process is responsible for the numerous bizarre features we see. We are hoping to make some more progress in the next few months.”

Example of banded terrain. Compare the relatively fresh appearance of the bands with the older terrain seen to the left of this sub-image. (NASA/JPL/University of Arizona/N. Thomas et al.)

This hypothesis is also in line with the possibility of Hellas Basin having once been a giant lake.

“Together with the observations of isolated areas and the lack of obvious caldera(s), it is difficult to envisage a volcanic origin for these features and we currently tend towards a mechanism involving ice,” Thomas stated in an abstract of a presentation given at the Europlanet Conference in 2010.

Read the full abstract here, and see this and more high-resolution images from Mars on the HiRISE website.

Posted on by Jason Major

Shaking Up Theories Of Earth’s Formation

Earth may not have formed quite like once thought (Image: NASA/Suomi NPP)

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Researchers from The Australian National University are suggesting that Earth didn’t form as previously thought, shaking up some long-standing hypotheses of our planet’s origins right down to the core — literally.

Ian Campbell and Hugh O’Neill, both professors at ANU’s Research School for Earth Sciences, have challenged the concept that Earth formed from the same material as the Sun — and thus has a “chondritic” composition — an idea that has been assumed accurate by planetary scientists for quite some time.

 

Chondrite meteorites are composed of spherical chondrules, which formed in the solar nebula before the asteroids. (NASA)

Chondrites are meteorites that were formed from the solar nebula that surrounded the Sun over 4.6 billion years ago. They are valuable to scientists because of their direct relationship with the early Solar System and the primordial material they contain.

“For decades it has been assumed that the Earth had the same composition as the Sun, as long the most volatile elements like hydrogen are excluded,” O’Neill said. “This theory is based on the idea that everything in the solar system in general has the same composition. Since the Sun comprises 99 per cent of the solar system, this composition is essentially that of the Sun.”

Instead, they propose that our planet was formed through the collision of larger planet-sized bodies, bodies that had already grown massive enough themselves to develop an outer shell.

This scenario is supported by over 20 years of research by Campbell on columns of hot rock that rise from Earth’s core, called mantle plumes. Campbell discovered no evidence for “hidden reservoirs” of heat-producing elements such as uranium and thorium that had been assumed to exist, had Earth actually formed from chondritic material.

“Mantle plumes simply don’t release enough heat for these reservoirs to exist. As a consequence the Earth simply does not have the same composition as chondrites or the Sun,” Campbell said.

The outer shell of early Earth, containing heat-producing elements obtained from the impacting smaller planets, would have been eroded away by all the collisions.

“This produced an Earth that has fewer heat producing elements than chondritic meteorites, which explains why the Earth doesn’t have the same chemical composition,” O’Neill said.

The team’s paper has been published in the journal Nature. Read the press release from The Australian National University here.

Posted on by Jason Major

Postcards From Saturn

Saturn's second-largest moon Rhea, in front of the rings and a blurred Epimetheus (or Janus) whizzing behind. Acquired March 29, 2012.

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Over the past few days NASA’s Cassini spacecraft has performed flybys of several of Saturn’s moons. From the ostentatious Enceladus with its icy geysers to the rugged relief of Rhea, the sharp peaks of Dione’s frigid craters and even diminutive Janus, Cassini has once again returned a stack of stunning views from the Saturnian system, nearly 815 million miles from home.

Check out some of the images, and wish you were there!

110-mile (177-km) -wide Janus in front of Saturn's night side.
A crescent-lit Enceladus shows off its jets. (South is up.)
Enceladus' fractured surface is some of the most reflective terrain in the Solar System.
Wide-angle view of Rhea, Saturn and Mimas
Crater peak on icy Dione

And here’s a color-composite of Janus I assembled from three raw images taken in ultraviolet, green and infrared color channels. The results were tweaked to make it a little more true-color as what we might see with our limited human vision:

Color composite of Janus in front of Saturn, made from raw images taken in UV, green and IR color filters. (NASA/JPL/SSI/J. Major)

“Though we’ve been in orbit around Saturn for nearly 8 years now, we still continue to image these moons for mapping purposes and, in the case of Enceladus, to learn as much as we can about its famous jets and the subterranean, organic-rich, salty, liquid water chamber from which we believe they erupt.”

– Carolyn Porco, Cassini Imaging Team leader

For more images from Cassini, check out JPL’s mission site and the CICLOPS imaging lab site here.

Image credits: NASA/JPL/Space Science Institute.

Posted on by Jason Major

Photo Treat: Enceladus, Titan and Saturn’s Rings

Color-composite image from Cassini raw data acquired on March 12, 2012. (NASA/JPL/SSI/J. Major)

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Little Enceladus and enormous Titan are seen on either side of Saturn’s rings in this image, a color-composite made from raw images acquired by Cassini on March 12, 2012. The original images were taken in red, green and blue color channels, and with a little Photoshop editing I combined them into a roughly true-color view of what Cassini saw as it passed within 1,045,591 km of Enceladus.

Follow along with the Cassini mission here.

Image credit: NASA/JPL/Space Science Institute. Edited by Jason Major.

Posted on by Jason Major

A Peek at a Pitch-Black Pit

A rimless pit crater within the crater Tolstoj

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MESSENGER captured this high-resolution image of an elongated pit crater within the floor of the 355-km (220-mile) -wide crater Tolstoj on Mercury on Jan. 11, 2012. The low angle of sun illumination puts the interior of the pit crater into deep shadow, making it appear bottomless.

Pit craters are not caused by impacts, but rather by the collapse of the roof of an underground magma chamber. They are characterized by the lack of a rim or surrounding ejecta blankets, and are often not circular in shape.

Since the floor of Tolstoj crater is thought to have once been flooded by lava, a pit crater is not out of place here.

The presence of such craters on Mercury indicates past volcanic activity on Mercury contributing to the planet’s evolution.

Read more on the MESSENGER mission website here.

Image credit: : NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington