Universe Today

May 10, 2011April 13, 2022 by Ken Kremer

NASA Sets May 16 for Last Launch of Endeavour; Atlantis Slips to July

Space Shuttle Endeavour is now set to launch on May16 at 8:56 a.m. EDT from Pad 39 A following launch scrub on April 29, 2011. Critical APU fuel line heaters in the aft section of the orbiter failed in the final hours of the countdown. This close up view was taken while I was standing next to the orbiter in March. Endeavour and crew will deliver the $2 Billion Alpha Magnetic Spectrometer to the International Space Station which seeks to unveil the Unknown and uncover the birth of the Universe. Credit: Ken Kremer

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KENNEDY SPACE CENTER – NASA managers set May 16 as the new launch date for the final flight of Space Shuttle Endeavour after technicians completed work to rewire and retest a switchbox in the orbiters aft compartment. Shuttle managers ordered the repair work following a heater malfunction that forced NASA officials to call off the planned April 29 launch.

At a briefing for reporters today (May 9) at NASA’s Kennedy Space Center in Florida, Shuttle managers Mike Moses and Mike Leinbach announced that Endeavour’s last liftoff is now targeted for 8:56 a.m. EDT on Monday, May 16.

“Right now, we’re in good shape,” said Shuttle Launch Director Mike Leinbach.

“Endeavour’s looking good, the team is upbeat. I went to the meeting this morning and they’re ready to go. Hopefully, this time the heaters will work and we’ll be able to launch on time next Monday morning.”

Repairs to Space Shuttle Endeavour have been completed at launch pad 39 A. Arrow shows location of access door used by technicians to swap out the faulty Aft Load Control Assembly (ALCA-2) near the main engines and install new wiring. Credit: Ken Kremer

The STS-134 mission is the penultimate flight of the space shuttle program and will deliver the $2 Billion Alpha Magnetic Spectrometer to the International Space Station.

Endeavour’s last launch attempt on April 29 was scrubbed about four hours prior to blastoff when critical hydrazine fuel line heaters failed to turn on inside one of the orbiters three auxiliary power units (APU’s).

Technicians have been working around the clock to resolve the problems and determined that the likely cause of the heater failure was an electrical short inside the ALCA -2 load control assembly box located in the aft section of the shuttle (see photo).

They installed about 20 feet of new wiring, a new ALCA box and then retested all related systems over the past week and a half.

“We’ve replaced everything except the heaters, and we’ve wrung those out with at least five separate checks and full functionals afterwards and now have extremely high confidence that the problem is no longer on the ship or in any of the electronics,” said Mike Moses, the Shuttle launch integration manager at the Kennedy Space Center.

At the NASA Shuttle Logistics Depot in Cape Canaveral, Florida, the Load Control Assembly-2 (LCA-2) is uncovered for testing. Located in space shuttle Endeavour's aft avionics bay 5, the LCA-2 distributes power to nine shuttle systems. LCA-2 was replaced and all systems were retested. Credit: NASA/Kim Shiflett

The APU’s control the shuttles hydraulics which power the steering of the main engines, wings, wheels and rudders during ascent and re-entry. The three units must all be fully functional before NASA can commit to any shuttle launch as part of the launch commit criteria (LCC). If the heaters fail during flight, the hydrazine can freeze and clog the fuel lines and render the hydraulics inoperative. A rupture in the lines could result in toxic hydrazine leaking into the shuttles aft engine compartment.

The potential launch window for Endeavour’s final flight extends through May 26, except for May 21.

The all veteran six man crew led by Shuttle Commander Mark Kelly is due to fly to the Cape on Thursday, May 12 from their training base in Houston. The STS-134 mission has been officially extended to 16 days from 14 days and will include 4 spacewalks.

The launch countdown will commence on Friday, May 13 from the beginning of the nominal 41 hour countdown sequence.

As a consequence of Endeavour’s delays, the launch of the very final shuttle mission of Space Shuttle Atlantis will likely be delayed to mid-July, although Moses and Leinbach did not give a specific target date.

NPR Radio interview including Ken here:
Shuttle Fixes Will Take At Least One Week

STS-134 crew plans to fly back to the Kennedy Space Center on May 12 in anticipation of May 16 launch. Here they posed for photographers at Shuttle Landing Facility on April 26 ahead of the scrubbed first launch attempt on April 29, 2011. Mission Specialists Greg Chamitoff, Andrew Feustel, Commander Mark Kelly, Pilot Greg H. Johnson, Mission Specialist Mike Fincke and European Space Agency astronaut Roberto Vittori.. Credit: Ken Kremer

Space Shuttle managers Mike Moses (Launch Integration) and Mike Leinbach (Launch Director) at the Kennedy Space Center. Credit: Ken Kremer

Ken Kremer and Mike Leinbach (right) discuss Endeavour at a prior news briefing at the Kennedy Space Center.
Credit: Stephen Clark/Spaceflight Now

May 9, 2011December 24, 2015 by Tammy Plotner

Catch Seven Planets Now!

Planetary Alignment in Tasmania by Shevill Mathers

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No… What you’re looking at isn’t fireflies caught in the trees – but planets! Thanks to a little haze in Tasmania, incomparable sky shot artist, Shevill Mathers, was able to capture four planets lined up neatly before the dawn. One of the most beautiful facets of this image is that this is (with the exception of daily movement) how it appears to the unaided eye. Over the last couple of weeks, we’ve watched the inner planets gather along the ecliptic just before dawn… but even just a day makes a dramatic difference in their positions. We see it with our own eyes and we know it’s natural – but what makes it happen? Let’s find out…

Even though it’s been over 240 years since a very cool dude named Johannes Kepler was born, some of the laws he laid down about planetary motion still hold true today. Despite the fact he could have been jailed for supporting the Sun-centered Copernican theory, Kepler was teaching a class about the conjunction of Saturn and Jupiter when he realized that regular polygons bound one inscribed and one circumscribed circle at definite ratios, which, he reasoned, might be the geometrical basis of the Universe. From these conclusions, Kepler gave us three laws:

1. The orbit of every planet is an ellipse with the sun at one of the foci.

2. A line joining a planet and the sun sweeps out equal areas during equal intervals of time. (Suppose a planet takes one day to travel from point A to B. The lines from the Sun to A and B, together with the planet orbit, will define a (roughly triangular) area. This same amount of area will be formed every day regardless of where in its orbit the planet is. This means that the planet moves faster when it is closer to the Sun.) This is because the sun’s gravity accelerates the planet as it falls toward the Sun, and decelerates it on the way back out, but Kepler did not know that reason.

3. The squares of the orbital periods of planets are directly proportional to the cubes of the semi-major axis of the orbits. Thus, not only does the length of the orbit increase with distance, the orbital speed decreases, so that the increase of the orbital period is more than proportional.

Each day the second law is clearly demonstrated as the inner planets quickly change position because they are closer to the Sun. But what about the outer planets? They’re obeying the third law and will barely change positions over the next couple of months. Let’s take a look…

may10a — Location Map of Planets on May 10, 2011

Right now is the best time of year to catch all the planets in our solar system in the same night. After sunset, grab Saturn… before dawn you’ll find Uranus and Neptune hanging around in the constellation of Aquarius. As skies begin to brighten, you’ll find Mars, Jupiter, Venus and Mercury rising in progression just ahead of the Sun. What a wonderful way to celebrate the morning… by standing on Earth and checking out planetary motion!

May 9, 2011January 18, 2016 by Nancy Atkinson

Astronomy Cast EP. 220: Mass Extinction Events

The Earth seems like a safe place, most of the time. But we have evidence of terrible catastrophes in the ancient past, times when almost all life on Earth was wiped out in a geologic instant. What could have caused so much devastation? And will something like this happen again?

Click here to download the episode.
Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

Mass Extinction Events shownotes and transcript.

May 9, 2011December 29, 2015 by Nancy Atkinson

Carnival of Space #196

This week’s Carnival of Space is hosted by Amy Teitel over at Vintage Space.

Click here to read the Carnival of Space #196.

And if you’re interested in looking back, here’s an archive to all the past Carnivals of Space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, sign up to be a host. Send an email to the above address.

May 9, 2011December 24, 2015 by Jason Major

A Cometary Case for Titan’s Atmosphere

Ancient comets may have created Titan's nitrogen-rich atmosphere

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Titan is a fascinating world to planetary scientists. Although it’s a moon of Saturn it boasts an opaque atmosphere ten times thicker than Earth’s and a hydrologic cycle similar to our own – except with frigid liquid methane as the key component instead of water. Titan has even been called a living model of early Earth, even insofar as containing large amounts of nitrogen in its atmosphere much like our own. Scientists have wondered at the source of Titan’s nitrogen-rich atmosphere, and now a team at the University of Tokyo has offered up an intriguing answer: it may have come from comets.

Traditional models have assumed that Titan’s atmosphere was created by volcanic activity or the effect of solar UV radiation. But these rely on Titan having been much warmer in the past than it is now…a scenario that Cassini mission scientists don’t think is the case.

New research suggests that comet impacts during a period called the Late Heavy Bombardment – a time nearly 4 billion years ago when collisions by large bodies such as comets and asteroids were occurring regularly among worlds in our solar system – may have generated Titan’s nitrogen atmosphere. By firing lasers into ammonia-and-water-ice material similar to what would have been found on primordial Titan, researchers saw that nitrogen was a typical result. Over the millennia these impacts could have created enough nitrogen to cover the moon in a dense haze, forming the thick atmosphere we see today.

“We propose that Titan’s nitrogen atmosphere formed after accretion, by the conversion from ammonia that was already present on Titan during the period of late heavy bombardment about four billion years ago.”

– Yasuhito Sekine et al., University of Tokyo, Japan

This model, if true, would also mean that the source of Titan’s nitrogen would be different than that of other outer worlds, like Pluto, and even inner planets like our own.

See the published results in the journal Nature, or read more on NewScientist.com.

Top image is a combination of a color-composite of Titan made from raw Cassini data taken on October 12, 2010 and a recolored infrared image of the comet Siding Spring, taken by NASA’s WISE observatory on January 10, 2010. The background stars were also taken by the Cassini orbiter. NASA / JPL / SSI and Caltech/UCLA. Edited by J. Major.

Note: the image at top is not scientifically accurate…the comet’s tail would be, based on the lighting of Titan, pointing more to the ten o’clock position as well as forward toward the viewer’s left shoulder. This would make it ‘look’ as if it were going the opposite direction though, away from Titan, and so I went with the more immediately decipherable version seen here. To see a more “realistic” version, click here.

May 8, 2011April 13, 2022 by Ken Kremer

Atlas V Roars to Space with Sophisticated New Missile Warning Surveillance Satellite

Blast off of sophisticated SBIRS GEO-1 satellite aboard an Atlas V rocket from Space Launch Complex-41 at Cape Canaveral Air Force Station at 2:10 p.m. EDT on May 7, 2011. Credit: Alan Walters/awaltersphoto.com

[/caption]CAPE CANAVERAL – An Atlas V rocket carrying a highly sophisticated Space-Based Infrared System (SBIRS) GEO-1 satellite for the United States Air Force lifted off from the seaside Space Launch Complex-41 at 2:10 p.m. EDT on Saturday (May 7) into a gorgeous clear blue sky following a one day delay due to cloudy weather conditions surrounding the Florida space coast on Friday.

SBIRS GEO-1 is the maiden satellite in a new constellation of next generation military space probes that will provide US military forces with an early warning of missile launches that could pose a threat to US national security.

Atlas V rocket roars to space with SBIRS GEO-1 satellite Pad 41 at Cape Canaveral Air Force Station on May 7, 2011.
Credit: Alan Walters/awaltersphoto.com

“Today, we launched the next generation missile warning capability. It’s taken a lot of hard work by the government-industry team and we couldn’t be more proud. We look forward to this satellite providing superb capabilities for many years to come,” said General Gen. William Shelton, Air Force Space Command commander in a statement.

The planned quartet of SBIRS satellites will deliver a quantum leap in infrared event detection and reporting compared to the current generation of orbiting Defense Support Program (DSP) satellites, according to Michael Friedman of Lockheed Martin in an interview with Universe Today at the Kennedy Space Center (KSC).

“The SBIRS GEO satellites will have both a scanning and starring sensor with faster revisit rates. They will be able to detect missile launches from the earliest stages of the boost phase and track the missiles to determine their trajectory and potential impact points,” said Friedman.

“SBIRS can see targets quicker and characterize the actual missile,’” explained Steve Tatum of Lockheed Martin at KSC.

In addition to providing improved and persistent missile warning capabilities in a global arena, SBIRS will simultaneously support missile defense, technical intelligence, battlespace awareness and defense of the US homeland.

“The 10,000 pound SBIRS GEO-1 satellite is the size of two Hummers. About 9000 people in 23 states were involved in constructing the satellite.”

“SBIRS GEO-2 will launch in the next year or two,” Friedman told me.

“GEO-2 is built and undergoing testing now,” added Tatum.

The $1.2 Billion SBIRS satellite was launched into a 22,000 mile high Geosynchronous orbit by the 189 foot tall Atlas V rocket. The Atlas rocket was in the 401 vehicle configuration with no solid rocket motors and includes a 4-meter diameter payload fairing.

The first stage was powered by the RD AMROSS RD-180 engine and the Centaur upper stage was powered by a single Pratt & Whitney Rocketdyne RL-10A engine.

SBIRS GEO-1 satellite bolted atop Atlas V Centaur rocket at Space Launch Complex 41 prior to launch. SBIRS is housed inside a 4 meter diameter Payload Fairing. Credit: Ken Kremer

The Atlas V rocket was built and launched by United Launch Alliance (ULA). This marks the 50th successful launch for ULA since the company was formed in December 2006.

“With this launch, ULA continues to demonstrate its commitment to 100 percent mission success,” said Michael Gass, ULA President and CEO. “This milestone is a testament to the dedicated employees that for every mission deliver excellence, best value and continuous improvement to our customers.”

Read my Atlas V SBIRS preview story here:
Atlas Rocket Poised for Blast Off with Advanced Missile Early Warning Spy Satellite

SBIRS GEO-1 Launch Photo Album by the Universe Today team of Ken Kremer and Alan Walters:

Atlas V rocket and bird soar skywards at Florida Space Coast
Liftoff of Atlas V rocket with SBIRS GEO-1 satellite as an Egret flies into camera field of view on May 7, 2011 at 2:10 p.m. EDT. View from the Press Site at the Kennedy Space Center:
Credit: Ken Kremer -- kenkremer.com

Atlas V rocket soars off pad 41 with SBIRS GEO-1 satellite for the US Air Force as another bird flies into camera field of view on May 7, 2011 at 2:10 p.m. EDT. View from the Press Site at the Kennedy Space Center: Credit: Ken Kremer

Atlas V SBIRS GEO-1 launch from Cape Canaveral on May 7, 2011. Credit: Alan Walters/awaltersphoto.com

Exhaust trail from Atlas V SBIRS GEO-1 launch on May 7, 2011. Credit: Ken Kremer

Ken Kremer with Atlas V rocket and SBIRS GEO-1 satellite at Launch Pad 41, prior to blast off from Cape Canaveral Air Force Station. Credit: Ken Kremer

May 8, 2011December 24, 2015 by Steve Nerlich

Astronomy Without A Telescope – Planet Spotting

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The Extrasolar Planets Encyclopedia counted 548 confirmed extrasolar planets at 6 May 2011, while the NASA Star and Exoplanet Database (updated weekly) was today reporting 535. These are confirmed findings and the counts will significantly increase as more candidate exoplanets are assessed. For example, there were the 1,235 candidates announced by the Kepler mission in February, including 54 that may be in a habitable zone.

So what techniques are brought to bear to come up with these findings?

Pulsar timing – A pulsar is a neutron star with a polar jet roughly aligned with Earth. As the star spins and a jet comes into the line of sight of Earth, we detect an extremely regular pulse of light. Indeed, it is so regular that a slight wobble in the star’s motion, due to it possessing planets, is detectable.

The first extrasolar planets (i.e. exoplanets) were found in this way, actually three of them, around the pulsar PSR B1257+12 in 1992. Of course, this technique is only useful for finding planets around pulsars, none of which could be considered habitable – at least by current definitions – and, in all, only 4 such pulsar planets have been confirmed to date.

To look for planets around main sequence stars, we have…

The radial velocity method – This is similar in principle to detection via pulsar timing anomalies, where a planet or planets shift their star back and forth as they orbit, causing tiny changes in the star’s velocity relative to the Earth. These changes are generally measured as shifts in a star’s spectral lines, detectable via Doppler spectrometry, although detection through astrometry (direct detection of minute shifts in a star’s position in the sky) is also possible.

To date, the radial velocity method has been the most productive method for exoplanet detection (finding 500 of the 548), although it most frequently picks up massive planets in close stellar orbits (i.e. hot Jupiters) – and as a consequence these planets are over-represented in the current confirmed exoplanet population. Also, in isolation, the method is only effective up to about 160 light years from Earth – and only gives you the minimum mass, not the size, of the exoplanet.

To determine a planet’s size, you can use…

The transit method – The transit method is effective at both detecting exoplanets and determining their diameter – although it has a high rate of false positives. A star with a transiting planet, which partially blocks its light, is by definition a variable star. However, there are many different reasons why a star may be variable – many of which do not involve a transiting planet.

For this reason, the radial velocity method is often used to confirm a transit method finding. Thus, although 128 planets are attributed to the transit method – these are also part of the 500 counted for the radial velocity method. The radial velocity method gives you the planet’s mass – and the transit method gives you its size (diameter) – and with both these measures you can get the planet’s density. The planet’s orbital period (by either method) also gives you the distance of the exoplanet from its star, by Kepler’s (that is Johannes’) Third Law. And this is how we can determine whether a planet is in a star’s habitable zone.

It is also possible, from consideration of tiny variations in transit periodicity (i.e regularity) and the duration of transit, to identify additional smaller planets (in fact 8 have been found via this method, or 12 if you include pulsar timing detections). With increased sensitivity in the future, it may also be possible to identify exomoons in this way.

The transit method can also allow a spectroscopic analysis of a planet’s atmosphere. So, a key goal here is to find an Earth analogue in a habitable zone, then examine its atmosphere and monitor its electromagnetic broadcasts – in other words, scan for life signs.

Direct imaging of exoplanet Beta Pictoris b - assisted by nulling interferometry which removes Beta Pictoris' starlight from the image. The red flares are a circumstellar debris disk heated by the star. Credit: ESO.

To find planets in wider orbits, you could try…

Direct imaging – This is challenging since a planet is a faint light source near a very bright light source (the star). Nonetheless, 24 have been found this way so far. Nulling interferometry, where the starlight from two observations is effectively cancelled out through destructive interference, is an effective way to detect any fainter light sources normally hidden by the star’s light.

Gravitational lensing – A star can create a narrow gravitational lens and hence magnify a distant light source – and if a planet around that star is in just the right position to slightly skew this lensing effect, it can make its presence known. Such an event is relatively rare – and then has to be confirmed through repeated observations. Nonetheless, this method has detected 12 so far, which include smaller planets in wide orbits such as OGLE-2005-BLG-390Lb.

These current techniques are not expected to deliver a complete census of all planets within current observational boundaries, but do offer us an impression of how many there may be out there. It has been speculatively estimated from the scant data available so far, that there may be 50 billion planets within our galaxy. However, a number of definitional issues remain to be fully thought through, such as where you draw the line between a planet versus a brown dwarf. The Extrasolar Planets Encyclopedia currently set the limit at 20 Jupiter masses.

Anyhow, 548 confirmed exoplanets for only 19 years of planet spotting is not bad going. And the search continues.

Further reading:
The Extrasolar Planets Encyclopedia
The NASA Star and Exoplanet Database (NStED)
Methods of detecting extrasolar planets
The Kepler mission.

May 7, 2011April 26, 2016 by Jason Major

More Evidence of Liquid Erosion on Mars?

Possible water-formed gullies cut through sedimentary layers in Terby Crater

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Terby Crater, a 170-km-wide (100-mile-wide) crater located on the northern edge of the vast Hellas Planitia basin in Mars’ southern hemisphere, is edged by variable-toned layers of sedimentary rock – possibly laid down over millennia of submersion beneath standing water. This image (false-color) from the HiRISE camera aboard the Mars Reconnaissance Orbiter shows a portion of Terby’s northern wall with what clearly looks like liquid-formed gullies slicing through the rock layers, branching from the upper levels into a main channel that flows downward, depositing a fan of material at the wall’s base.

But, looks can be deceiving…

Terby Crater. Credit: NASA/JPL/University of Arizona

Dry processes – especially on Mars, where large regions have been bone-dry for many millions of years – can often create the same effects on the landscape as those caused by running water. Windblown Martian sand and repetitive dry landslides can etch rock in much the same way as liquid water, given enough time. But the feature seen above in Terby seem to planetary scientists to be most likely the result of liquid erosion… especially considering that the sedimentary layers themselves seem to contain clay materials, which only form in the presence of liquid water. Is it possible that some water existed beneath Mars’ surface long after the planet’s surface dried out? Or that it’s still there? Only future exploration will tell for sure.

“While formation by liquid water is one of the proposed mechanisms for gully formation on Mars, there are others, such as gravity-driven mass-wasting (like a landslide) that don’t require the presence of liquid water. This is still an open question that scientists are actively pursuing.”

– Nicole Baugh, HiRISE Targeting Specialist

Terby Crater was once on the short list of potential landing sites for the new Mars Science Laboratory (aka Curiosity) rover but has since been removed from consideration. Still, it may one day be visited by a future robotic mission and have its gullies further explored from ground level.

Click here to see the original image on the HiRISE site.

Image credit: NASA / JPL / University of Arizona

May 6, 2011December 24, 2015 by Jon Voisey

Update on Gliese 581d’s Habitability

An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra. Credit: NASA

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When last we checked in on Gliese 581d, a team from the University of Paris had suggested that the popular exoplanet, Gliese 581d may be habitable. This super-Earth found itself just on the edge of the Goldilocks zone which could make liquid water present on the surface under the right atmospheric conditions. However, the team’s work was based on one dimensional simulations of a column of hypothetical atmospheres on the day side of the planet. To have a better understanding of what Gliese 581d might be like, a three dimensional simulation was in order. Fortunately, a new study from the same team has investigated the possibility with just such an investigation.

The new investigation was called for because Gliese 581d is suspected to be tidally locked, much like Mercury is in our own solar system. If so, this would create a permanent night side on the planet. On this side, the temperatures would be significantly lower and gasses such as CO₂ and H₂O may find themselves in a region where they could no longer remain gaseous, freezing into ice crystals on the surface. Since that surface would never see the light of day, they could not be heated and released back into the atmosphere, thereby depleting the planet of greenhouse gasses necessary to warm the planet, causing what astronomers call an “atmospheric collapse.”

To conduct their simulation the team assumed that the climate was dominated by the greenhouse effects of CO₂ and H₂O since this is true for all rocky planets with significant atmospheres in our solar system. As with their previous study, they performed several iterations, each with varying atmospheric pressures and compositions. For atmospheres less than 10 bars, the simulations suggested that the atmosphere would collapse, either on the dark side of the planet, or near the poles. Past this, the effects of greenhouse gasses prevented the freezing of the atmosphere and it became stable. Some ice formation still occurred in the stable models where some of the CO₂ would freeze in the upper atmosphere, forming clouds in much the same way it does on Mars. However, this had a net warming effect of ~12°C.

In other simulations, the team added in oceans of liquid water which would help to moderate the climate. Another effect of this was that the vaporization of water from these oceans also produced warming as it can serve as a greenhouse gas, but the formation of clouds could decrease the global temperature since water clouds increase the albedo of the planet, especially in the red region of the spectra which is the most prevalent form of light from the parent star, a red dwarf. However, as with models without oceans, the tipping point for stable atmospheres tended to be around 10 bars of pressure. Under that, “cooling effects dominated and runaway glaciation occurred, followed by atmospheric collapse.” Above 20 bars, the additional trapping of heat from the water vapor significantly increased temperatures compared to an entirely rocky planet.

The conclusion is that Gliese 581d is potentially habitable. The potential for surface water exists for a “wide range of plausible cases”. Ultimately, they all depend on the precise thickness and composition of any atmosphere. Since the planet does not transit the star, spectral analysis through transmission of starlight through the atmosphere will not be possible. Yet the team suggests that, since the Gliese 581 system is relatively close to Earth (only 20 lightyears), it may be possible to observe the spectra directly in the infrared portion of the spectra using future generations of instruments. Should the observations match the synthetic spectra predicted for the various habitable planets, this would be taken as strong evidence for the habitability of the planet.

May 6, 2011December 24, 2015 by Jon Voisey

A Newly Discovered Planetary Nebula Teaches Us About Galactic Composition

Determining the chemical distribution of the galaxy is a tricky business. The ideal method is spectroscopy but since high quality spectroscopy takes bright targets, the number of potential targets is somewhat reduced. Stars seem like logical choices, but due to differential separation during formation, they don’t provide a true description of the interstellar medium. Clouds of gas and dust are the best choice, but must be illuminated by star formation. Another option is to search for newly formed planetary nebulae which are in the process of enriching the interstellar medium.

A new paper does just this, discovering a new planetary nebula in hopes of mapping the chemical abundance of the galaxy. The new nebula is almost the exact opposite direction of the galactic center when viewed from Earth. It lies at a distance of about 13 kpc (42,400 lightyears) from Earth making it one of the most distant planetary nebulae from the galactic center for which a distance has been determined and currently, the furthest with a measured chemical abundance.

The nebula was originally recorded on images taken by the INT Photometric Hα Survey (IPHAS) in 2003 but the automated program for detecting such objects initially missed the nebula due to its relatively large angular size (10 arcseconds). It was subsequently caught on visual inspection of the mosaics. Follow-up spectroscopy was conducted from 2005 to 2010 and reveal that the nebula is quite regular for planetary nebula, containing strong emission from hydrogen, nitrogen, oxygen, and silicon. The rate of expansion combined with its physical size suggests an age of nearly 18,000 years.

This newly discovered nebula provides a rare data point for the chemical abundance for the outer portions of the galaxy. While the galaxy is known to be enriched towards the galactic center, there has been debate about how quickly, if at all, it falls towards the galactic edge where star formation, and thus, enrichment, is less common. While there aren’t enough known nebulae to determine just yet (only four others are known at similar distances), this planetary nebula suggests that the abundance levels off in the galactic outskirts.

The authors also note that this nebula, as well as potentially the others, aren’t native to the Milky Way. They lie near a structure known as the Monoceros Ring, which is a stream of stars believed to be stretched out as the Milky Way devours the Canis Major Dwarf Galaxy.