A Good Reason to Wake Up at Dawn

Summer is a good time to relax, sleep late, enjoy a break from school or work.  Waking before sunrise is just not done.

This summer is a little different.  To find out why, set your alarm for dawn.

Every morning this July, the two brightest planets in the solar system will put on a show before sunrise.  Look out any east-facing window to see Venus and Jupiter, shining side by side, so close together you can hide them behind your outstretched palm.  It's a great way to start the day.

 On the 4th of July, Venus will be passing dead-center through the Hyades cluster, a loose grouping of stars 153 light years from Earth.   Using binoculars, scan around the bright planet; you'll see dozens of stars scattered across the velvety-black sky. The temporary addition of Venus will make it seem that a supernova has gone off in the cluster.

Three mornings later, on July 7th, Venus and Jupiter line up with Aldebaran, the bright red eye of Taurus the Bull.  Aldebaran is a red giant star of first magnitude.  Together with Venus and Jupiter, it forms an almost perfect vertical line in the brightening dawn sky.

The best, however, is yet to come.

On July 9th, Venus and Aldebaran converge to form an eye catching planet-star pair.  Scarcely more than a degree of arc will separate the two celestial bodies as Jupiter looks down from overhead.

And then, on July 15th, a 12% crescent Moon joins the show, forming a bright celestial triangle with Venus and Jupiter.

The slender arms of the crescent cradle a ghostly image of the full Moon.  That's caused by Earthshine, sunlight reflected from our own planet onto the otherwise dark lunar landscape.

A crescent Moon with Earthshine is considered to be one of the prettiest sights in the heavens.  A crescent Moon with Earthshine plus Venus and Jupiter--that's worth waking up for even in the middle of summer vacation.

Stellar Flare Blasts Exoplanet

An international team of astronomers using data from NASA's Hubble Space Telescope has made an unparalleled observation, detecting significant changes in the atmosphere of a planet located beyond our solar system.

The scientists conclude the atmospheric variations occurred in response to a powerful eruption on the planet's host star, an event observed by NASA's Swift satellite.  The stellar flare, which hit the planet like 3 million X-flares from our own sun, blasted material from the planet's atmosphere at a rate of at least 1,000 tons per second.

The multiwavelength coverage by Hubble and Swift has given us an unprecedented view of the interaction between a flare on an active star and the atmosphere of a giant planet," said lead researcher Alain Lecavelier des Etangs at the Paris Institute of Astrophysics (IAP), part of the French National Scientific Research Center located at Pierre and Marie Curie University in Paris.

The exoplanet is HD 189733b, a gas giant similar to Jupiter, but about 14 percent larger and more massive. The planet circles its star at a distance of only 3 million miles, or about 30 times closer than Earth's distance from the sun, and completes an orbit every 2.2 days. Its star, named HD 189733A, is about 80 percent the size and mass of our sun.

Astronomers classify the planet as a "hot Jupiter." Previous Hubble observations show that the planet's deep atmosphere reaches a temperature of about 1,900 degrees Fahrenheit (1,030 C).

HD 189733b periodically passes across, or transits, its parent star, and these events give astronomers an opportunity to probe its atmosphere and environment. In a previous study, a group led by Lecavelier des Etangs used Hubble to show that hydrogen gas was escaping from the planet's upper atmosphere. The finding made HD 189733b only the second-known "evaporating" exoplanet at the time.

The system is just 63 light-years away, so close that its star can be seen with binoculars near the famous Dumbbell Nebula. This makes HD 189733b an ideal target for studying the processes that drive atmospheric escape.

"Astronomers have been debating the details of atmospheric evaporation for years, and studying HD 189733b is our best opportunity for understanding the process," said Vincent Bourrier, a doctoral student at IAP and a team member on the new study.

In April 2010, the researchers observed a single transit using Hubble's Space Telescope Imaging Spectrograph (STIS), but they detected no trace of the planet's atmosphere. Follow-up observations in September 2011 showed a surprising reversal, with striking evidence that a plume of gas was streaming away from the exoplanet at 300,000 mph. At least 1,000 tons of gas were leaving the planet's atmosphere every second.

This turn of events was explained by data from Swift's X-ray Telescope. On Sept. 7, 2011, just eight hours before Hubble was scheduled to observe the transit, Swift was monitoring the star when it unleashed a powerful flare.

"The planet's close proximity to the star means it was struck by a blast of X-rays tens of thousands of times stronger than the Earth suffers even during an X-class solar flare, the strongest category," said co-author Peter Wheatley, a physicist at the University of Warwick in England. After accounting for the planet's enormous size, the team notes that HD 189733b encountered about 3 million times as many X-rays as Earth receives from a solar flare at the threshold of the X class.

http://science.nasa.gov

Evidence Mounts for Ice in Shackleton Crater

According to data from NASA's Lunar Reconnaissance Orbiter (LRO), ice may make up as much as 22 percent of the surface material in Shackleton crater at the Moon's south pole.

The huge crater, named after the Antarctic explorer Ernest Shackleton, is two miles deep and more than 12 miles wide. The small tilt of the lunar spin axis means Shackleton's interior is permanently dark and very cold..  Researchers have long thought that ice might collect  there.

When a team of NASA and university scientists used LRO's laser altimeter to examine the floor of Shackleton crater, they found it to be brighter than the floors of other nearby craters around the South Pole. This is consistent with the presence of small amounts of reflective ice preserved by cold and darkness. The findings are published in today's edition of the journal Nature.

 In addition to the possible evidence of ice, the group's map of Shackleton revealed a remarkably preserved crater that has remained relatively unscathed since its formation more than three billion years ago. The crater's floor is itself pocked with several small craters, which may have formed as part of the collision that created Shackleton.

"The crater's interior is extremely rugged," said Maria Zuber, the team's lead investigator from the Massachusetts Institute of Technology in Cambridge in Mass. "It would not be easy to crawl around in there."

While the crater's floor was relatively bright, Zuber and her colleagues observed that its walls were even brighter. The finding was at first puzzling. Scientists had thought that if ice were anywhere in a crater, it would be on the floor, where no direct sunlight penetrates. The upper walls of Shackleton crater are occasionally illuminated, which could evaporate any ice that accumulates.

"The brightness measurements have been puzzling us since two summers ago," said Gregory Neumann of NASA's Goddard Space Flight Center in Greenbelt, Md., a co-author on the paper.

A theory offered by the team to explain the puzzle is that "moonquakes"-- seismic shaking brought on by meteorite impacts or gravitational tides from Earth -- may have caused Shackleton's walls to slough off older, darker soil, revealing newer, brighter soil underneath. Zuber's team's ultra-high-resolution map provides strong evidence for ice on both the crater's floor and walls.

"There may be multiple explanations for the observed brightness throughout the crater," said Zuber. "For example, newer material may be exposed along its walls, while ice may be mixed in with its floor."

http://science.nasa.gov