Artist's concept of MESSENGER in orbit around Mercury. Courtesy of NASA
After two years of doing the loop-the-loop around Mercury, MESSENGER has unveiled a bunch of surprises from Mercury — the closest planet to the Sun.
The spacecraft launched in 2004 and made three flybys of the planet before settling into orbit two years ago today. Incredibly, MESSENGER is only the second NASA probe to visit Mercury; the first one, Mariner 10, only flew by a few times in the 1970s. It was an incredible feat for the time, but we didn’t even have a complete map of Mercury before MESSENGER arrived at the planet.
So, what have scientists found in MESSENGER’s two years in orbit? Tales of sulfur, organic materials and iron, it turns out.
Mercury’s south pole has a weak spot
Magnetic field lines differ at Mercury’s north and south poles As a result of the north-south asymmetry in Mercury’s internal magnetic field, the geometry of magnetic field lines is different in Mercury’s north and south polar regions. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
The magnetic field lines converge differently at the north and south poles of Mercury. What does this mean? There’s a larger “hole” at the south pole for charged particles to do their thing to the surface of Mercury. At the time this information was released, NASA said it’s possible that space weathering or erosion would be different at the north and south poles because of this. Charged particles on the surface would also add to Mercury’s wispy atmosphere.
How the atmosphere changes according to distance from the sun
Comparison of neutral sodium observed during MESSENGER’s second and third Mercury flybys. Credit: NASA
Wondering about the atmosphere on Mercury? It depends on the season, and also the element. The scientists found striking changes in calcium, magnesium and sodium when the planet was closer to and further from the sun.
“A striking illustration of what we call ‘seasonal’ effects in Mercury’s exosphere is that the neutral sodium tail, so prominent in the first two flybys, is 10 to 20 times less intense in emission and significantly reduced in extent,” said participating scientist Ron Vervack, of the Johns Hopkins University Applied Physics Laboratory in 2009. “This difference is related to expected variations in solar radiation pressure as Mercury moves in its orbit and demonstrates why Mercury’s exosphere is one of the most dynamic in the solar system.”
Discovery of water ice and organics
A radar image of Mercury’s north polar region is shown superposed on a mosaic of MESSENGER images of the same area. All of the larger polar deposits are located on the floors or walls of impact craters. Deposits farther from the pole are seen to be concentrated on the north-facing sides of craters. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/National Astronomy and Ionosphere Center, Arecibo Observatory
Late in 2012, NASA finally was able to corroborate some science results from about 20 years ago. Scientists on Earth saw “radar bright” images from Mercury in the 1990s, implying that there was ice and organic materials at the poles. MESSENGER finally confirmed that through three separate lines of investigation that were published in Science in 2012. Scientists estimated the planet holds between 100 billion and 1 trillion tons of water ice, perhaps as deep as 20 meters in some places. “Water ice passed three challenging tests and we know of no other compound that matches the characteristics we have measured with the MESSENGER spacecraft,” said MESSENGER principal investigator Sean Solomon in a NASA briefing.
Mercury has a big iron core
The internal structure of Mercury is very different from that of the Earth. The core is a much larger part of the whole planet in Mercury and it also has a solid iron-sulfur cover. As a result, the mantle and crust on Mercury are much thinner than on the Earth. Credit: Case Western Reserve University
While scientists knew before that Mercury has an iron core, the sheer size of it surprised scientists. At 85%, the proportion of the core to the rest of the planet dwarfs its rocky solar system companions. Further, scientists measured Mercury’s gravity. From that, they were surprised to see that the planet had a partially liquid core. “The planet is sufficiently small that at one time many scientists thought the interior should have cooled to the point that the core would be solid,” stated Case Western Reserve University’s Steven A. Hauck II, a co-author of a paper on the topic that appeared in Science Express.
The surface is sulfur-rich
A global view of Mercury, as seen by MESSENGER. Credit: NASA
At some point in Mercury’s history, it’s possible that it could have had lavas erupt and sprinkle the surface with sulfur, magnesium and similar materials. At any rate, what is known for sure is there is quite a bit of sulfur on Mercury’s surface. “None of the other terrestrial planets have such high levels of sulfur. We are seeing about ten times the amount of sulfur than on Earth and Mars,” said paper author Shoshana Weider of the Carnegie Institution of Washington.
The Wreath Nebula (Barnard 3) glows green in space in this Wide-field Infrared Survey Explorer (WISE) image. Credit: NASA/JPL-Caltech/UCLA
While a quest for green beer in space would be difficult, we’re happy to report there are other ways you can celebrate Saint Patrick’s Day while looking at the night sky. Just check out the nebulae and aurorae in these pictures!
A word of caution, these pictures are taken by cameras that expose light for a very long time, sometimes using different filters, to bring out the colors. A nebula, for example, seen with our own eyes does not look quite as stunning.
The picture above shows the Wreath Nebula, which apparently is filled with warm dust bits that are about the same composition as smog.
RCW 120. Credit: NASA/JPL-Caltech
Here’s a picture of a “Green Ring” Nebula; the NASA press release is worth a read for the hilarious Green Lantern references. But besides the science fiction, there is some neat science in action here: “The green color represents infrared light coming from tiny dust grains called polycyclic aromatic hydrocarbons,” NASA writes. “These small grains have been destroyed inside the bubble. The red color inside the ring shows slightly larger, hotter dust grains, heated by the massive stars.”
A portion of the Lagoon nebula imaged by the Gemini South telescope with the Gemini Multi-Object Spectrograph. Credit: Julia I. Arias and Rodolfo H. Barbá Departamento de Física, Universidad de La Serena (Chile), and ICATE-CONICET (Argentina).
You can even see hints of green in the Lagoon Nebula picture above. Using a filter that picks up green (sulfur) emission, the astronomers ferreted out a bit of emerald.
An October 2012 picture from Jason Arhns in Alaska, which he calls a “ghost flame.” Credit: Jason Arhns
If you live far enough north or south, you occasionally get to see aurorae dancing across the sky. These events, sometimes known as the Northern Lights or Southern Lights, occur due to interactions between the sun’s particles and the Earth’s upper atmosphere. We had some green stunners in October 2012 after a solar flare pushed a bunch of these particles in Earth’s direction. Most of the light you see in auroras comes from oxygen atoms being “excited” from the interaction with the sun’s particles; green occurs at higher altitudes, and red at lower ones.
Light curve of different stars.
One object that can’t glow green in space, however, is a star. Stellar colors depend on the surface of the star. Blue stars, the hottest ones, are at about 12,000 Kelvin and red stars, the coolest ones, are less than 3,500 Kelvin. (The sun is about in the middle, at 6,800 Kelvin, as it emits white light.)
As Universe Today publisher Fraser Cain pointed out in a past post, the only way a green star could be possible is if the light curve peaks at green. That doesn’t work, however: “If you make the star hotter, it just gets bluer,” he wrote. “And if you make a star cooler, it just becomes orange and then redder. There’s no way to have a light curve that makes a star look green.” Check out more details here.
Comet Pan-STARRS thrills Dutch observers of the Night Sky on March 15, 2013 shortly after sunset. Shot with a Canon 60D camera and Canon 100/400 mm lens, exposure time 15 seconds, ISO 300 Credit: Rob van Mackelenbergh
Comet Pan-STARRS thrills Dutch observers of the Night Sky on March 14, 2013 shortly after sunset- note the rich hues. Shot with a Canon 60D camera and Canon 100/400 mm lens, exposure time 2 seconds, ISO 800. Credit: Rob van Mackelenbergh See viewing guide and sky maps below Update – see readers photo below[/caption]
Comet Pan-STARRS (C/2011 L4) is exciting amateur astronomers observing the night sky worldwide as it becomes visible in the northern latitudes after sunset. And now it’s wowing crowds in Europe and all over Holland – north to south.
Check out the beautiful, richly hued new photos of Comet Pan-STARRS captured on March 14, 2013 by Dutch astrophotographer Rob van Mackelenbergh.
“I took these photos in the southern part of the Netherlands on Thursday evening, March 14, at around 7:45 pm Dutch time with my Canon 60 D camera.”
“I was observing from the grounds of our astronomy club – “Sterrenwacht Halley” – named in honor of Halley’s Comet.”
Comet Pan-STARRS is a non-periodic comet from the Oort Cloud that was discovered in June 2011 by the Pan-STARRS telescope located near the summit of the Hawaiian Island of Maui.
The comet just reached perihelion – closest approach to the Sun – on March 10, 2013. It passed closest to Earth on March 5 and has an orbital period of 106,000 years.
Comet Pan-STARRS from Holland on March 14, 2013 at about 7:45 PM, shortly after sunset – Canon 60D camera, Canon 100/400 mm lens, exposure time 2 seconds, ISO 800. Credit: Rob van Mackelenbergh
“Over 30 people were watching with me and they were all very excited, looking with binoculars and cameras. People were cheering. They were so excited to see the comet. But it was very cold, about minus 2 C,” said Mackelenbergh.
The “Sterrenwacht Halley” Observatory was built in 1987 and houses a Planetarium and a Celestron C14 Schmidt-Cassegrain telescope. It’s located about 50 km from the border with Belgium, near Den Bosch – the capitol city of southern Holland.
Comet Pan-STARRS was photographed from Sterrenwacht Halley – or ‘Halley Observatory” in Holland. Credit: Rob van Mackelenbergh
“It was hard to see the comet with the naked eye. But we were able to watch it for about 45 minutes altogether in the west, after the sun set.”
“The sky was completely clear except for a few scattered clouds near the horizon. After the comet set, we went inside the observatory for a general lecture about Comets and especially Comets Pan-STARRS and ISON because most of the people were not aware about this year’s pair of bright comets.”
“So everyone was lucky to see Comet Pan-STARRS because suddenly the sky cleared of thick clouds!”
Comet Pan-STARRS from Holland on March 14, 2013 at about 7:45 PM, shortly after sunset – Canon 60D camera, Canon 100/400 mm lens, exposure time 2 seconds, ISO 800. Credit: Rob van Mackelenbergh
“In the past I also saw Comet Halley and Comet Hale-Bopp, but these are my first ever comet photos and I’m really excited !”
“I hope to see Comet Pan-STARRS again in the coming days when the sky is clear,” Mackelenbergh told me.
Over the next 2 weeks or so the sunset comet may grow in brightness even as it recedes from Earth into darker skies. Right now it’s about magnitude 0.2.
So keep looking with your binoculars; look west for up to 1 to 2 hours after sunset – and keep your eyes peeled.
See a readers photo of sunset Comet Pan-STARRS below
Comet Pan-STARRS viewing graphic from NASAComet Pan-Starrs Sky Map. Viewing guide to find the comet low in the horizon after sunset.Credit: Spaceweather.com
Enter to win a free copy of the Phases of the Moon App brought to you by Universe Today.
We’re giving away 10 copies of Phases of the Moon for iPhone/iPad.
Want to know the current phase of the Moon at all times? Perhaps you need to do some stargazing or astrophotography, or you really need to debunk some nonsense theories about full Moon madness… then check out our handy mobile app – available on iPhone or Android.
Here are the features:
Beautiful images of the Moon were made by NASA from data collected by the Lunar Reconnaissance Orbiter.
Full internal simulation of the Moon’s position and phase. See the current date, phase name, distance and illumination percentage.
Swipe left and right to move forward or backwards in time to see what the Moon will look like in the future or past.
Click a button to take you to the next full Moon.
You can also access a calendar that shows you the phase of the Moon for any date in the future.
New 2013 features include total lunar eclipses, live Wallpaper and Widgets (for Android), and social sharing
The latest version of the app is running a full model of the Moon’s orbit and phases, displaying a scientifically accurate simulation of the Moon’s exact phase, size, distance and amount of illumination.
We’ve just done a major update to the app, extending the support to iPhone, and completely rebuilding the Android edition to be smoother and more stable on the wide range of devices.
You can swipe the Moon back and forth to see how the Moon’s distance and illumination change over time, or jump to the next full Moon, or see the Moon’s phase at any point in the future. The Android version is especially smooth, and kind of hypnotic as you change the phase.
In order to be entered into the giveaway drawing, just put your email address into the box at the bottom of this post (where it says “Enter the Giveaway”) before Saturday, March 23, 2013. We’ll send you a confirmation email, so you’ll need to click that to be entered into the drawing.
Thank you for your interest. This giveaway is now closed.
If you are not lucky enough to win a promo code, you can purchase a copy for $.99 on either Google Play or the iTunes Store, and help support Universe Today.
A new study describes how the Kepler team aims to remove pseudo-planets from its database. A pseudo-planet can be caused by the superposition of a foreground bright constant target star, and background fainter multiple star systems as shown in the above artist sketch (image credit: regulus36/devianart).
Observations by the Kepler satellite have advanced our knowledge of stars and their orbiting planets, yielding more than 100 confirmed planets and about 3,000 candidates. However, orbiting planets may not be the source for a fraction of those detections.
“There are many things in the sky that can produce transit-like signals that are not planets, and thus we must be sure to identify what really is a planet detected by Kepler,” Stephen Bryson told Universe Today. NASA Ames Research Center scientists Bryson and Jon Jenkins (also at the SETI Institute) are the lead authors on a new paper that aims to identify pseudo-planets detected by Kepler.
Small eclipses present in Kepler brightness measurements for a star (a lightcurve) may be indicative of an orbiting planet blocking light from its host star (see image below). However, under certain circumstances binary stars can mimic that signature.
Consider a Kepler target that is actually a chance superposition of a bright star and a fainter eclipsing binary system, whereby the objects lie at different distances along the sight-line. The figure below illustrates that their combined light can produce a lightcurve that is similar to a transiting planet. The bright foreground star dilutes the typically large eclipses produced by the binary system.
Left, the lightcurve for a star featuring a transiting planet, whereby the planet blocks a minute fraction of the host star’s light (image credit: Institute for Astronomy, University of Hawaii at Manoa). Right, the combined light from a foreground bright star and a fainter eclipsing binary system can mimic a transiting planet (image credit: chart and assembly, D. Majaess – cropped stellar graphics from Collier Cameron 2012, Nature).
“Most of the time these eclipsing binaries are not exactly aligned with our target star,” Bryson added, “and we can carefully examine the pixels to discover that the location of the transit signal is not the target star.” The team developed algorithms to identify pseudo-planets when the stars are individually resolved. Tagging spurious planet detections is important since there are numerous candidates, and yet limited observing time for follow-up efforts.
The team has been refining those algorithms as knowledge of the satellite’s in situ behavior increases. “These algorithms have been developed and used over the last four years. Some details of the techniques in the paper are new and will appear in future versions of the Kepler [software processing] pipeline,” said Bryson.
However, if multiple stars fall within the same pixel they are not individually resolved by Kepler, and a separate approach is required to infer their presence. Consider the example highlighted in the image below, where several stars were unresolved by Kepler yet appear in higher resolution images. The matter is exacerbated in part because Kepler’s spatial resolution is not optimal, and thus multiple stars may be confused as a single object. By contrast, certain ground-based telescopes can achieve ~20 times Kepler’s spatial resolution when adaptive optics are implemented.
High-resolution images (right panel) can reveal stars that were unresolved in lower-resolution images (left panel, e.g., Kepler). Unresolved stars dilute eclipses caused by transiting planets, and in certain cases can strongly bias the derived parameters (image credit: right panel from Adams et al. 2012, arXiv/AJ – left panel, image blurred to provide a lower-resolution glimpse of the target, assembly by D. Majaess).
Adams et al. 2012 obtained high-resolution images of 90 Kepler targets, one of which is highlighted above. That team noted that, “Close companions … are of particular concern … Of the [90 Kepler targets surveyed] 20% have at least one companion within [half a Kepler pixel].” The high-resolution images were acquired via the MMT observatory (shown below) and the Palomar Hale-200-inch telescope.
Obviously, the resolution problem becomes more acute when observing rich stellar fields (high densities), such as near the plane of our Galaxy.
“Background eclipsing binaries account for as many as 35% of all planet-like transit signals when we are looking near the Milky Way, because there are many stars in the background,” Bryson told Universe Today. “When we look away from the Milky Way the fraction of background eclipsing binaries falls to about 10% of all planet-like transit signals because there are far fewer background stars of all types.”
However, regarding Kepler’s coarser resolution Bryson underscored that, “[it is] expected with such a large field telescope.” Kepler’s large field is certainly advantageous, as it permits the satellite to monitor 100,000+ stars over more than 100 square degrees of field.
The adaptive optics (AO) system at the MMT observatory provides astronomers with high-resolution images to search the vicinity of Kepler planet candidates for contaminating stars (image credit: Thomas Stalcup, SPIE).
Radial velocity measurements are an ideal means for evaluating planet candidates (and to help yield the mass). The data are pertinent since velocity shifts occur in the spectrum of the host star owing to the planet’s gravity. However, Adams et al. 2012 note that “Many of these objects do not have … radial velocity measurements because of the amount of observing time required, particularly for small planets around relatively faint stars. Another method is needed to confirm these types of planets … High-resolution images are thus a crucial component of any transit follow-up program.”
Identifying unresolved stars is crucial for yet another reason. Note that the fundamental parameters determined for a transiting planet depend in part on the fraction of the host star’s light that is obscured (the eclipse depth). However, if multiple unresolved stars exist they will contribute to the overall brightness, and hence the observed planet eclipse will be diluted and underestimated (see figure 2, above). Indeed, Adams et al. 2012 note that, “Corrections to the planetary parameters based on nearby [contaminating] stars can range from a few to tens of percents, making high resolution images an important tool to understanding the true sizes of other discovered worlds.”
The case of K00098 is a prime example underscoring the importance of identifying unresolved contaminating stars. K00098 features two rather bright stars that were unresolved and unknown prior to the acquisition of high-resolution images. Consequently, previously determined parameters for that star’s transiting planet were incorrect. Concerning K00098, Adams et al. 2012 remarked that, “for K00098, the dilution [of the eclipse depth] … were substantial: the [planet’s] radius increased by 10%, the mass by 60% … and the density changed by 25% [from that published]. Without high resolution images, we would have had a very inaccurate picture of this planet.”
Low and high-resolution images of stars in the galaxy M33. The bright object detected in the low-resolution image is actually several stars, as indicated by the higher-resolution image (right). A similar effect occurs when comparing Kepler (lower-resolution) and AO images (higher-resolution). A single Kepler target can actually constitute multiple stars seen along the sight-line (image credit: Mochejska et al. 2001, arXiv).
Incidentally, unaccounted for light from unresolved stars isn’t merely a problem for exoplanet studies. The issue is rather pertinent when researching the cosmic distance scale and the Hubble constant (expansion rate of the Universe). Consider the images above which feature the same field in M33. The image exhibited on the left is from a ground-based facility, whereas the higher-resolution image displayed on the right is from the Hubble Space Telescope (HST). The brightest star at the center of the image is a Cepheid variable star, which is a pulsating star that is used to establish distances to galaxies. In turn those distances are subsequently employed to determine the Hubble constant. The HST image reveals stars that are unresolved in the ground-based image, and thus the distance inferred from that observation is compromised since the Cepheid appears (spuriously) brighter than it should be.
“Blending [e.g., added light caused by unresolved stars] leads to systematically low distances to galaxies observed with the HST, and therefore to systematically high estimates of the Hubble constant,” remarked Mochejska et al. 2004. However, there is an ongoing debate concerning the importance of such an effect (Ferrarese et al. 2000, Mochejska et al. 2001).
In sum, numerous groups are developing methods to identify pseudo-planets in the Kepler database. Given the large sample and sizable investment of time required to confirm a planet candidate: such efforts are important (e.g., Bryson et al. 2013). Data from the Kepler mission have helped advance our understanding of stars and their orbiting planets, and more is yet to come. If you’d like to help the Kepler team identify planets around other stars: join the Planet Hunters citizen science project.
Apollo 13's dangerous explosion in 1970 inspired a movie, released in 1995, that starred (left to right) Bill Paxton, Kevin Bacon and Tom Hanks. Credit: Universal Pictures
Space is a dangerous and sometimes fatal business, but happily there were moments where a situation happened and the astronauts were able to recover.
An example: today (March 16) in 1966, Neil Armstrong and Dave Scott were just starting the Gemini 8 mission. They latched on to an Agena target in the hopes of doing some docking maneuvers. Then the spacecraft started spinning inexplicably.
They undocked and found themselves tumbling once per second while still out of reach of ground stations. A thruster was stuck open. Quick-thinking Armstrong engaged the landing system and stabilized the spacecraft. This cut the mission short, but saved the astronauts’ lives.
Gemini 8’s Agena target before a stuck thruster on the spacecraft put the astronauts in a terrifying tumble. Credit: NASA
Here are some other scary moments that astronauts in space faced, and survived:
Friendship 7: False landing bag indicator (1962)
Astronaut John Glenn views stencilling used as a model to paint the words “Friendship 7” on his spacecraft. Credit: NASA
John Glenn was only the third American in space, so you can imagine the amount of media attention he received during his three-orbit flight. NASA received an indication that his landing bag had deployed while he was still in space. Friendship 7’s Mercury spacecraft had its landing cushion underneath the heat shield, so NASA feared it had ripped away. Officials eventually informed Glenn to keep his retrorocket package strapped to the spacecraft during re-entry, rather than jettisoning it, in the hopes the package would keep the heat shield on. Glenn arrived home safely. It turned out to be a false indicator.
Apollo 11: Empty fuel tank (1969)
Apollo 11’s Eagle spacecraft, as seen from fellow spaceship Columbia. Credit: NASA
Shortly after Neil Armstrong announced “Houston, Tranquility Base, here, the Eagle has landed” during Apollo 11, capsule communicator Charlie Duke answered, “Roger, Tranquility. We copy you on the ground. You got a bunch of guys about to turn blue. We’re breathing again. Thanks a lot.” They weren’t holding their breath just because it was the first landing on the moon; Armstrong was navigating a spacecraft that was almost out of fuel. The spacecraft Eagle overshot its landing and Armstrong did a series of maneuvers to put it on relatively flat ground. Accounts say he had less than 30 seconds of fuel when he landed on July 20, 1969.
Apollo 12: Lightning strike (1969)
Apollo 12’s launch in 1969, moments before the rocket was struck by lightning. Credit: NASA
Moments after Apollo 12 headed from ground towards orbit, a lightning bolt hit the rocket and caused the spacecraft to go into what appeared to be a sort of zombie mode. The rocket was still flying, but the astronauts (and people on the ground) were unsure what to do. Scrambling, one controller suggested a command that essentially reset the spacecraft, and Apollo 12 was on its way. NASA did take some time to do some double-checking in orbit, to be sure, before carrying on with the rest of the mission. The agency also changed procedures about launching in stormy weather.
Apollo 13: Oxygen tank explosion (1970)
Evidence of the Apollo 13 explosion on the service module. Credit: NASA
The astronauts of Apollo 13 performed a routine stir of the oxygen tanks on April 13, 1970. That’s when they felt the spacecraft shudder around them, and warning lights lit up. It turned out that an oxygen tank, damaged through a series of ground errors, had exploded in the service module that fed the spacecraft Odyssey, damaging some of its systems. The astronauts survived for days on minimal power in Aquarius, the healthy lunar module that was originally supposed to land on the moon. They arrived home exhausted and cold, but very much alive.
Apollo-Soyuz Test Project: Toxic vapours during landing (1975)
The Apollo command module used in the Apollo-Soyuz Test Project, during recovery. Credit: NASA
The Apollo-Soyuz Test Project was supposed to test out how well American and Russian systems (and people) would work together in space. Using an Apollo command module and a Russian Soyuz, astronauts and cosmonauts met in orbit and marked the first mission between the two nations. That almost ended in tragedy when the Americans returned to Earth and their spacecraft was inadvertently flooded with vapours from the thruster fuel. “I started to grunt-breathe to make sure I got pressure in my lungs to keep my head clear. I looked over at Vance [Brand] and he was just hanging in his straps. He was unconscious,” recalled commander Deke Slayton, in a NASA history book about the event. Slayton ensured the entire crew had oxygen masks, Brand revived quickly, and the mission ended shortly afterwards.
Mir: The fire (1997)
Jerry Linenger dons a mask during his mission on Mir in 1997. Credit: NASA
The crew on Mir was igniting a perchlorate canister for supplemental oxygen when it unexpectedly ignited. As they scrambled to put out the fire, NASA astronaut Jerry Linenger discovered at least one oxygen mask on board were malfunctioning as well. The crew managed to contain the fire quickly. Even though it affected life aboard the station for a while afterwards, the crew survived, did not need to evacuate, and helped NASA learn lessons that they still use aboard the International Space Station today.
STS-51F: Abort to orbit (1985)
STS-51F aborted to orbit during its launch. Credit: NASA
The crew of space shuttle Challenger endured two aborts on this mission. The first one took place at T-3 seconds on July 12, when a coolant valve in one of the shuttle’s engines malfunctioned. NASA fixed the problem, only to face another abort situation shortly after liftoff on July 29. One of the engines shut down too early, forcing the crew to abort to orbit. The crew was able to carry on its mission, however, including many science experiments aboard Spacelab.
STS-114: Foam hitting Discovery (2005)
Discovery during STS-114, as seen from the International Space Station. CREDIT: NASA
When Discovery lifted off in 2005, the fate of the entire shuttle program was resting upon its shoulders. NASA had implemented a series of fixes after the Columbia disaster of 2003, including redesigning the process that led to foam shedding off Columbia’s external tank and breaching the shuttle wing. Wayne Hale, a senior official in the shuttle program, later recalled his terror when he heard of more foam loss on Discovery: “I think that must have been the worst call of my life. Once earlier I had gotten a call that my child had been in an auto accident and was being taken to the hospital in an ambulance. That was a bad call. This was worse.” The foam, thankfully, struck nothing crucial and the crew survived. NASA later discovered the cracks in the foam are linked to changes in temperature the tank undergoes, and made more changes in time for a much more successful mission in 2006.
We’ve probably missed some scary moments in space, so which ones do you recall?
Three members of the Expedition 34 crew undocked from the International Space Station a day later than originally planned on Friday due to bad weather in the landing area in Kazakhstan, but returned safely to Earth, despite continuing cold, foggy weather. The deteriorating weather conditions allowed only two of 12 search and rescue helicopters to land at the touchdown site because of heavy clouds and fog. NASA TV was unable to show the actual landing after the Soyuz capsule descended into the dense fog. Continue reading “Expedition 34 Crew Gets a Foggy Welcome Home”
Gale crater's central peak as it might look under Earthly lighting (NASA/JPL-Caltech/MSSS)
Ahh — there’s nothing like a beautiful sunny day in Gale crater! The rusty sand crunching beneath your wheels, a gentle breeze blowing at a balmy 6º C (43º F), Mount Sharp rising in the distance into a clear blue sky… wait, did I just say blue sky?
I sure did. But no worries — Mars hasn’t sprouted a nitrogen-and-oxygen atmosphere overnight. The image above is a crop from a panoramic mosaic made of images from NASA’s Curiosity rover, showing Gale crater’s central peak Mount Sharp (or Aeolis Mons, if you prefer the official moniker.) Don’t let the blue sky fool you though — the lighting has been adjusted to look like a sunlit scene on Earth, if only to let geologists more easily refer to their own experience when studying the Martian landscape.
Click the image to see the full panorama, and a view of the same scene under more “natural” Martian lighting can be found below:
Aeolis Mons panorama seen in natural lighting (NASA/JPL-Caltech/MSSS)
According to JPL, in both versions the sky has been filled out by extrapolating color and brightness information from the portions of the sky that were captured in images of the terrain.
The elevation of Mt. Sharp compared to three mountains on Earth (NASA/JPL-Caltech/MSSS)
The component images were taken by the 100-millimeter-focal-length telephoto lens camera mounted on the right side of Curiosity’s remote sensing mast, during the 45th Martian day of the rover’s mission on Mars (Sept. 20, 2012).
Informally named after planetary scientist Robert Sharp by the MSL science team, the peak rises rises more than 3 miles (5 kilometers) above the floor of Gale crater.
See more news and images from the Curiosity rover here (and to find out what the latest weather conditions in Gale crater are visit MarsWeather.com here.)
A visualization of the “unseen” red dwarfs in the night sky. Credit: D. Aguilar & C. Pulliam (CfA)
As we’ve reported recently, the likelihood of findings habitable Earth-sized worlds just seems to keep getting better and better. But now the latest calculations from a new paper out this week are almost mind-bending. Using what the authors call a “very careful extrapolation” of the rate of small planets observed around M dwarf stars by the Kepler spacecraft, they estimate there could be upwards of 100 billion Earth-sized worlds in the habitable zones of M dwarf or red dwarf stars in our galaxy. And since the population of these stars themselves are estimated to be around 100 billion in the Milky Way, that’s – on average – an Earth-sized world for every red dwarf star in our galaxy.
Whoa.
And since our solar system is surrounded by red dwarfs – very cool, very dim stars not visible to the naked eye (less than a thousandth the brightness of the Sun) — these worlds could be close by, perhaps as close as 7 light-years away.
With the help of astronomer Darin Ragozzine, a postdoctoral associate at the University of Florida who works with the Kepler mission (see our Hangout interview with him last year), let’s take a look back at the recent findings that brought about this latest stunning projection.
Back in February, we reported on the findings from Courtney Dressing and Dave Charbonneau from the Center for Astrophysics that said about 6% of red dwarf stars could host Earth-size habitable planets. But since then, Dressing and Charbonneau realized they had a bug in their code and they have revised the frequency to 15%, not 6%. That more than doubles the estimates.
Then, just this week we reported how Ravi Kopparapu from at Penn State University and the Virtual Planetary Lab at University of Washington suggested that the habitable zone around planets should be redefined, based on new, more precise data that puts the habitable zones farther away from the stars than previously thought. Applying the new habitable zone to red dwarfs pushes the fraction of red dwarfs having habitable planets closer to 50%.
The graphic shows optimistic and conservative habitable zone boundaries around cool, low mass stars. The numbers indicate the names of known Kepler planet candidates. Yellow color represents candidates with less than 1.4 times Earth-radius. Green color represents planet candidates between 1.4 and 2 Earth radius. Credit: Penn State.
But now, the new paper submitted to arXiv this week, “The Radius Distribution of Small Planets Around Cool Stars” by Tim Morton and Jonathan Swift (a grad student and postdoc from Caltech’s ExoLab) finds there is an additional correction to the numbers by Dressing and Charbonneau numbers.
“This is basically due to the fact that there are more small planets than we thought because Kepler isn’t yet sensitive to a large number that take longer to orbit,” Ragozzine told Universe Today. “Accounting for this effect and enhancing the calculation using some nice new statistical techniques, they estimate that the Dressing and Charbonneau numbers are actually too small by a factor of 2. This puts the number at 30% in the old habitable zone, and now up to about 100% in the new habitable zone.”
Now, it is important to point out a few things about this.
As Morton noted in an email to Universe Today, it’s important to realize that this is not yet a direct measurement of the habitable zone rate, “but it is what I would classify as a very careful extrapolation of the rate of small planets we have observed at shorter periods around M dwarfs.”
And as Ragozzine and Morton confirmed for us, all of these numbers are based on Kepler results only, and so far, while there confirmed planets around M dwarfs, there are none confirmed so far in the habitable zone.
“They do not use any results from Radial Velocity (HARPS, etc.),” Ragozzine said. “As such, these are all candidates and not planets. That is, the numbers are based on an assumption that most/all of the Kepler candidates are true planets. There are varying opinions about what the false positive rate would be, especially for this particular subset of stars, but there’s no question that the numbers may go down because some of these candidates turn out to be something else other than HZ Earth-size planets.”
Other caveats need to be considered, as well.
“Everyone needs to be careful about what “100%” means,” Ragozzine said. “It does not mean that every M dwarf has a HZ Earth-size planet. It means that, on average, there is 1 HZ-Earth size planet for every M dwarf. The difference comes from the fact that these small stars tend to have planets that come in packs of 3-5. If, on average, the number of planets per star is one, and the typical M star has 5 planets, then only 20% of M stars have planetary systems.”
The point is subtle but important. For example, if you want to plan new telescope missions to observe these planets, understanding their distribution is critical, Ragozzine said.
“I’m very interested in understanding what kinds of planetary systems host these planets as this opens a number of interesting scientific questions. Discerning their frequency and distribution are both valuable.”
Additionally, the new definition of the habitable zone from Kopparapu et al. makes a big difference.
As Ragozzine points out:
“This is really starting to point out that the definition of the HZ is based on mostly theoretical arguments that are hard to rigorously justify,” Ragozzine said. “For example, a recent paper came out showing that atmospheric pressure makes a big difference but there’s no way to estimate what the pressure will be on a distant world. (Even in the best cases, we can barely tell that the whole planet isn’t one giant puffy atmosphere.) Work by Kopparapu and others is clearly necessary and, from an astrobiological point of view, we have no choice but to use the best theory and assumptions available. Still, some of us in the field are starting to become really wary of the “H-word” (as Mike Brown calls it), wondering if it is just too speculative. Incidentally, I much, much prefer that these worlds be referred to as potentially habitable, since that’s really what we’re trying to say.”
However, Morten told Universe Today that he feels the biggest difference in their work was the careful extrapolation from short period planets to longer periods. “This is why we get occurrence rates for the smaller planets that are twice as large as Dressing or Kopparapu,” he said via email.
He also thinks the most interesting thing in their paper is not just the overall occurrence rate or the HZ occurrence rate even, but the fact that, for the first time, they’ve identified some interesting structure in the distribution of exoplanet radii.
“For example, we show that it appears that planets of roughly 1 Earth radius are actually the most common size of planet around these cool stars,” Morton said. “This makes some intuitive sense given the rocky bodies in our Solar System—there are two planets about the size of Earth, making it the most common size of small planet in our system too! Also, we find that there are lots and lots of planets around M dwarfs that are just beyond the detection threshold of current ground-based transiting surveys—this means that as more sensitive instruments and surveys are designed, we will just keep finding more and more of these exciting planets!”
But Ragozzine told us that even with all aforementioned caveats, the exciting thing is that the main gist of these new numbers probably won’t change much.
“No one is expecting that the answer will be different by more than a factor of a few – i.e., the true range is almost certainly between 30-300% and very likely between 70-130%,” Ragozzine said. “As the Kepler candidate list improves in quantity (due to new data), purity, and uniformity, the main goal will be to justify these statements and to significantly reduce that range.”
Another fun aspect is that this new work is being done by the young generation of astronomers, grad students and postdocs.
“I’m sure this group and others will continue producing great things… the exciting scientific results are just beginning!” Ragozzine said.
This image shows an aerial view of the Chajnantor Plateau, located at an altitude of 5000 meters in the Chilean Andes, where the array of ALMA antennas is located. Credit: Clem & Adri Bacri-Normier (wingsforscience.com)/ESO.
A new film called The View From Mars takes a look ALMA (Atacama Large Millimeter Array), the huge international telescope project that was inaugurated in Chile this week. It is located in the Atacama Desert, the driest place on Earth and an area that bears a striking resemblance to the Red Planet.
But the conditions there, with clear, dry skies, are perfect for astronomy. ALMA’s moveable group of 66 giant antennas do not detect visible light like conventional optical telescopes. Instead they work together to gather emissions from gas, dust and stars and make observations in millimeter wavelengths, using radio frequencies instead of visible light—with no need for darkness, so the stars can be studied around the clock. With these tools, astronomers will soon be able to look billions of years into the past, gazing at the formation of distant stars and galaxies.
“In doing so,” says filmmaker Jonathan de Villiers, “they’ll build a clearer picture of how our sun and our galaxy formed.”
