Bulge in Venus’ atmosphere likely caused by gravity waves

The massive bow wave is visible in the upper atmosphere of Venus in this infrared image

A massive, bow-shaped wave was spotted for the first time in the highest regions of Venus’ atmosphere, perplexing astronomers.

The structure was captured by the Japan Aerospace Exploration Agency (JAXA) in some of the first images returned by their Akatsuki orbiter following a troubled orbital insertion in late 2015. Using both infrared and UV imaging, researchers spotted the prominent feature in the planet’s upper atmosphere, where winds whip by in excess of 200 miles per hour. Any features spotted in the atmosphere should get carried along by the fierce winds, but this curved wave remained planted firmly in place, lasting for at least four days.

Planet-spanning

The wave extends for more than 6,000 miles, stretching nearly from pole to pole. It is marked by the presence of slightly warmer air in the upper portion of the planet’s thick atmosphere, some 40 miles above the surface. While small aberrations are common in the upper atmosphere, such a large feature, to say nothing of one that refuses to move, is highly uncommon.

Venus’ atmosphere is in a state of super-rotation, meaning it moves much faster than the planet does. Venus rotates very slowly on its axis, completing just one rotation every 243 Earth days — longer than it takes the planet to go around the sun. On Earth, winds move only 10 to 20 percent the speed of the planet at most, but on Venus they far outpace the planet’s stately spin.

Gravity Waves

The researchers believe that the enormous structure might be caused by so-called “gravity waves” in Venus’ atmosphere. Gravity waves (which are entirely different than gravitational waves), are upheavals in a planet’s atmosphere caused by winds colliding with features on the surface. In the case of Venus, mountainous features on the surface may be forcing winds into the upper atmosphere, where they slow down enough to create a lasting bow wave. Indeed, the atmospheric bulge is located above Aphrodite Terra, a continent-sized region of highlands. The researchers discuss their findings in a paper published Monday in Nature Geoscience.

An illustration of how gravity waves likely form on Venus. Surface winds are pushed upwards by topological features such as mountains into the upper atmosphere where they “break” like waves on a shore, slowing down high-altitude winds.

ESA

The bow wave was only spotted for four days near the beginning of Akatsuki’s mission. When researchers looked again a month later, it had disappeared. Scientists have observed the presence of gravity waves in the upper atmosphere of Venus before — the European Space Agency’s Venus Express orbiter found the telltale cloud shapes over the smaller Ishtar Terra region in 2014 — but those gravity waves were not nearly as large as the planet-spanning feature found by JAXA.

Our understanding of gravity waves is currently based on models of Earth’s atmosphere. On Venus, where the air is composed mainly of carbon dioxide and the atmospheric pressure is almost 100 times greater than that on Earth, the atmospheric dynamics are likely different. The waves could give astronomers another way to discern the terrain hidden beneath Venus’ thick layer of opaque clouds.

Signs of Modern Astronomy Seen in Ancient Babylon

Clay tablets, including one at the left, revealed that Babylonian astronomers employed a sort of precalculus to describe Jupiter’s motion across the night sky relative to distant background stars. They did this 15 centuries earlier than Europeans were first credited with making such measurements.CreditLeft to right: Trustees of the British Museum/Mathieu Ossendrijver; NASA

For people living in the ancient city of Babylon, Marduk was their patron god, and thus it is not a surprise that Babylonian astronomers took an interest in tracking the comings and goings of the planet Jupiter, which they regarded as a celestial manifestation of Marduk.

What is perhaps more surprising is the sophistication with which they tracked the planet, judging from inscriptions on a small clay tablet dating to between 350 B.C. and 50 B.C. The tablet, a couple of inches wide and a couple of inches tall, reveals that the Babylonian astronomers employed a sort of precalculus in describing Jupiter’s motion across the night sky relative to the distant background stars. Until now, credit for this kind of mathematical technique had gone to Europeans who lived some 15 centuries later.

“That is a truly astonishing find,” said Mathieu Ossendrijver, a professor at Humboldt University in Berlin, who describes his archaeological astronomy discovery in an article on Thursday in the journal Science.

“It’s a figure that describes a graph of velocity against time,” he said. “That is a highly modern concept.”

Mathematical calculations on four other tablets show that the Babylonians realized that the area under the curve on such a graph represented the distance traveled.

“I think it’s quite a remarkable discovery,” said Alexander Jones, a professor at the Institute for the Study of the Ancient World at New York University, who was not involved with the research. “It’s really quite clear from the text.”

Ancient Babylon, situated in what is now Iraq, south of Baghdad, was a thriving metropolis, a center of trade and science. Early Babylonian mathematicians who lived between 1800 B.C. and 1600 B.C. had figured out, for example, how to calculate the area of a trapezoid, and even how to divide a trapezoid into two smaller trapezoids of equal area.

For the most part, Babylonians used their mathematical skills for mundane calculations, like figuring out the size of a plot of land. But on some tablets from the later Babylonian period, there appear to be some trapezoid calculations related to astronomical observations.

In the 1950s, an Austrian-American mathematician and science historian, Otto E. Neugebauer, described two of them. Dr. Ossendrijver, in his recent research, turned up two more.

But it was not clear what the Babylonian astronomers were calculating.

A year ago, a visitor showed Dr. Ossendrijver a stack of photographs of Babylonian tablets that are now held by the British Museum in London. He saw a tablet he had not seen before. This tablet, with impressions of cuneiform script pressed into clay, did not mention trapezoids, but it recorded the motion of Jupiter, and the numbers matched those on the tablets with the trapezoid calculations.

“I was certain now it was Jupiter,” Dr. Ossendrijver said.

When Jupiter first appears in the night sky, it moves at a certain velocity relative to the background stars. Because Jupiter and Earth both constantly move in their orbits, to observers on Earth, Jupiter appears to slow down, and 120 days after it becomes visible, it comes to a standstill and reverses course.

In September, Dr. Ossendrijver went to the British Museum, where the tablets were taken in the late 19th century after being excavated. A close-up look of the new tablet confirmed it: The Babylonians were calculating the distance Jupiter traveled in the sky from its appearance to its position 60 days later. Using the technique of splitting a trapezoid into two smaller ones of equal area, they then figured out how long it took Jupiter to travel half that distance.

Dr. Ossendrijver said he did not know the astronomical or astrological motivation for these calculations.

It was an abstract concept not known elsewhere at the time. “Ancient Greek astronomers and mathematicians didn’t make plots of something against time,” Dr. Ossendrijver said. He said that until now, such calculations were not known until the 14th century by scholars in England and France. These mathematicians of the Middle Ages perhaps had seen some as yet unknown texts dating to Babylonian times, or they developed the same techniques independently.

“It anticipates integral calculus,” Dr. Ossendrijver said. “This is utterly familiar to any modern physicist or mathematician.”

Supernova observed colliding with its companion star

In this still from a simulation, a Type Ia supernova explodes (dark brown colour). The supernova material is ejected outwards at a velocity of about 10,000 kilometres/second. The ejected material then slams into its companion star (light blue colour). The violent collision produces an ultraviolet pulse that is emitted from the conical hole carved out by the companion star. Image credit: Daniel Kasen.
The origin of type Ia supernovae, the standard candles used to reveal the presence of dark energy in the universe, is one of astronomy’s most beguiling mysteries. Astronomers know they occur when a white dwarf explodes in a binary system with another star, but the properties of that second star — and how it triggers the explosion — have remained elusive for decades.

Now, a team of astronomers from the intermediate Palomar Transient Factory (iPTF), including those associated with UC Santa Barbara, have witnessed a supernova smashing into a nearby star, shocking it, and creating an ultraviolet glow that reveals the size of the companion. The discovery involved the rapid response and coordination of iPTF, NASA’s Swift satellite and the new capabilities of the Las Cumbres Observatory Global Telescope Network (LCOGT).

The supernova, named iPTF14atg, is located 300 million light-years away in the galaxy IC 831. The study, appearing in the May 21st issue of Nature, was led by graduate student Yi Cao of Caltech, but included physics postdoctoral fellows Iair Arcavi and Stefano Valenti, and physics faculty member Andrew Howell of UCSB and LCOGT.

In a type Ia supernova, a white dwarf star explodes after it gains matter from a companion star in the same binary star system. One of the leading theories is that the supernova happens when two white dwarf stars merge. But a competing theory says that the companion could be a normal or giant star that survives the explosion, although not without some damage. The supernova is expected to hit the companion star, creating a shock wave that glows in ultraviolet light. This had been theorised in 2010, but such an effect had never been seen. This and other factors led many to conclude that most type Ia supernovae arise from the mergers of two white dwarf stars.

“As you can imagine, I was fired up when I first saw a bright spot at the location of this supernova in the ultraviolet image,” first author Yi Cao said of seeing the ultraviolet flash. “I knew this was likely what we had been hoping for.”

LCOGT, a global network of robotic telescopes, was influential in obtaining early and regular data, allowing the researchers to determine the type and even the strange subclass of the supernova. Initially, the team was puzzled, said Arcavi.

“Hot, blue supernovae are not supposed to happen in old, dead galaxies,” he said. “And yet, as our robotic telescopes gathered the data, we watched in amazement as the blue supernova morphed into a type Ia supernova.”

Upon hearing about the supernova, the LCOGT team immediately triggered their worldwide fleet of robotic telescopes. As the Earth rotated, data was collected at different sites, depending on where it was nighttime and the observing conditions were ideal. Ultimately they combined data from LCOGT telescopes located in Texas, Hawaii and South Africa with data from Palomar and NASA’s Swift satellite to piece together the story of the supernova.

“As the data came in, I started to notice that this supernova was a weird one,” said Valenti. “It was a type Ia, but one with a slow-moving explosion.”

According to the researchers, the supernova belongs to a subclass of SNe Ia sometimes called SN 2002cx-like. These supernovae may even be partially failed or incomplete explosions. In a normal type Ia the entire white dwarf blows up, but this class may leave a piece behind.

There have been conflicting observations about the progenitors of type Ia supernovae. The new study builds on previous work by Howell and some of the study’s coauthors showing that the type Ia SN 2011fe was likely the result of a merger of two white dwarf stars, while the SN Ia PTF11kx seemed to have a red giant companion star.

Said Howell, “No wonder we’ve been so confused for decades. Apparently you can blow up stars in two different ways and still get nearly identical explosions.”

In fact, the study complements work by another postdoc and member of the supernova team at LCOGT and UCSB, Curtis McCully, who was not involved in the present study. He led a team of astronomers who announced in Nature in 2014 that they had found a progenitor on pre-explosion images from the Hubble Space Telescope for a similar SN 2002cx-like supernova, SN 2012Z. In that case, they think what they saw was the companion star, the star that in the case of iPTF14atg shocked the supernova.

“We are finally beginning to see how differences in the progenitor stars relate to differences in the explosion,” McCully said. “This is exciting because the better we understand the origin of type Ia supernovae, the better we can use them as standard candles for cosmology.”

The iPTF project is a scientific collaboration between Caltech; Los Alamos National Laboratory; the University of Wisconsin-Milwaukee; the Oskar Klein Center in Sweden; the Weizmann Institute of Science in Israel; the TANGO Program of the University System of Taiwan; and the Kavli Institute for the Physics and Mathematics of the Universe in Japan. The Caltech team is funded in part by the National Science Foundation.

LCOGT is a global network of 11 one-meter and two-meter telescopes with headquarters in Santa Barbara, California. It has telescopes in Hawaii, Texas, Australia, South Africa and Chile.

NASA’s WISE spacecraft discovers most luminous galaxy in universe

This artist's concept depicts the current record holder for the most luminous galaxy in the universe.

A remote galaxy shining with the light of more than 300 trillion Suns has been discovered using data from NASA’s Wide-field Infrared Survey Explorer (WISE). The galaxy is the most luminous found to date and belongs to a new class of objects recently discovered by WISE — extremely luminous infrared galaxies (ELIRGs).

“We are looking at a very intense phase of galaxy evolution,” said Chao-Wei Tsai of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “This dazzling light may be from the main growth spurt of the galaxy’s black hole.”

The brilliant galaxy, known as WISE J224607.57-052635.0, may have a behemoth black hole at its belly, gorging itself on gas. Supermassive black holes draw gas and matter into a disk around them, heating the disk to roaring temperatures of millions of degrees and blasting out high-energy, visible, ultraviolet, and X-ray light. The light is blocked by surrounding cocoons of dust. As the dust heats up, it radiates infrared light.

Immense black holes are common at the cores of galaxies, but finding one this big so “far back” in the cosmos is rare. Because light from the galaxy hosting the black hole has traveled 12.5 billion years to reach us, astronomers are seeing the object as it was in the distant past. The black hole was already billions of times the mass of our Sun when our universe was only a tenth of its present age of 13.8 billion years.

The new study outlines three reasons why the black holes in the ELIRGs could have grown so massive. First, they may have been born big. In other words, the “seeds,” or embryonic black holes, might be bigger than thought possible.

“How do you get an elephant?” asked Peter Eisenhardt from JPL. “One way is start with a baby elephant.”

The other two explanations involve either breaking or bending the theoretical limit of black hole feeding called the Eddington limit. When a black hole feeds, gas falls in and heats up, blasting out light. The pressure of the light actually pushes the gas away, creating a limit to how fast the black hole can continuously scarf down matter. If a black hole broke this limit, it could theoretically balloon in size at a breakneck pace. Black holes have previously been observed breaking this limit; however, the black hole in the study would have had to repeatedly break the limit to grow this large.

Alternatively, the black holes might just be bending this limit.

“Another way for a black hole to grow this big is for it to have gone on a sustained binge, consuming food faster than typically thought possible,” said Tsai. “This can happen if the black hole isn’t spinning that fast.”

If a black hole spins slowly enough, it won’t repel its meal as much. In the end, a slow-spinning black hole can gobble up more matter than a fast spinner.

“The massive black holes in ELIRGs could be gorging themselves on more matter for a longer period of time,” said Andrew Blain of the University of Leicester in the United Kingdom. “It’s like winning a hot-dog-eating contest lasting hundreds of millions of years.”

More research is needed to solve this puzzle of these dazzlingly luminous galaxies. The team has plans to better determine the masses of the central black holes. Knowing these objects’ true hefts will help reveal their history, as well as that of other galaxies, in this very crucial and frenzied chapter of our cosmos.

WISE has been finding more of these oddball galaxies in infrared images of the entire sky captured in 2010. By viewing the whole sky with more sensitivity than ever before, WISE has been able to catch rare cosmic specimens that might have been missed otherwise.

The new study reports a total of 20 new ELIRGs, including the most luminous galaxy found to date. These galaxies were not found earlier because of their distance, and because dust converts their powerful visible light into an incredible outpouring of infrared light.

“We found in a related study with WISE that as many as half of the most luminous galaxies only show up well in infrared light,” said Tsai.

Herschel and Planck find missing clue to galaxy cluster formation

The Planck all-sky map at submillimeter wavelengths (545 GHz). The band running through the middle corresponds to dust in our Milky Way Galaxy. The black dots indicate the location of the proto-cluster candidates identified by Planck and subsequently observed by Herschel. The inset images showcase some of the observations made by Herschel’s SPIRE instrument; the contours represent the density of galaxies.

By combining observations of the distant universe made with the European Space Agency’s (ESA) Herschel and Planck space observatories, cosmologists have discovered what could be the precursors of the vast clusters of galaxies that we see today. 

Galaxies like our Milky Way with its 100 billion stars are usually not found in isolation. In the universe today, 13.8 billion years after the Big Bang, many are in dense clusters of tens, hundreds, or even thousands of galaxies. 

However, these clusters have not always existed, and a key question in modern cosmology is how such massive structures assembled in the early universe. 

Pinpointing when and how they formed should provide insight into the process of galaxy cluster evolution, including the role played by dark matter in shaping these cosmic metropolises. 

Now, using the combined strengths of Herschel and Planck, astronomers have found objects in the distant universe seen at a time when it was only 3 billion years old that could be precursors of the clusters seen around us today.

Planck’s main goal was to provide the most precise map of the relic radiation of the Big Bang, the cosmic microwave background. To do so, it surveyed the entire sky in nine different wavelengths from the far-infrared to radio in order to eliminate foreground emission from our galaxy and others in the universe. 

But those foreground sources can be important in other fields of astronomy, and it was in Planck’s short-wavelength data that scientists were able to identify 234 bright sources with characteristics that suggested they were located in the distant early universe. 

Herschel then observed these objects across the far-infrared to submillimeter wavelength range but with much higher sensitivity and angular resolution. 

Herschel revealed that the vast majority of the Planck-detected sources are consistent with dense concentrations of galaxies in the early universe, vigorously forming new stars. 

Each of these young galaxies is seen to be converting gas and dust into stars at a rate of a few hundred to 1,500 times the mass of our Sun per year. By comparison, our Milky Way Galaxy today is producing stars at an average rate of just one solar mass per year. 

While the astronomers have not yet conclusively established the ages and luminosities of many of these newly discovered distant galaxy concentrations, they are the best candidates yet found for “protoclusters” — precursors of the large mature galaxy clusters we see in the universe today. 

“Hints of these kinds of objects had been found earlier in data from Herschel and other telescopes, but the all-sky capability of Planck revealed many more candidates for us to study,” said Hervé Dole of the Institut d’Astrophysique Spatiale, Orsay. 

“We still have a lot to learn about this new population, requiring further follow-up studies with other observatories. But we believe that they are a missing piece of cosmological structure formation.” 

“We are now preparing an extended catalog of possible protoclusters detected by Planck, which should help us identify even more of these objects,” said Ludovic Montier from the Institut de Recherche en Astrophysique et Planétologie, Toulouse. 

“This exciting result was possible thanks to the synergy between Herschel and Planck: rare objects could be identified from the Planck data covering the entire sky, and then Herschel was able to scrutinize them in finer detail,” said Göran Pilbratt from ESA. 

“Both space observatories completed their science observations in 2013, but their rich datasets will be exploited for plentiful new insights about the cosmos for years to come.” 

First pair of merging stars destined to become a supernova found

This artist’s impression shows the central part of the planetary nebula Henize 2-428. The core of this unique object consists of two white dwarf stars, each with a mass a little less than that of the Sun. They are expected to slowly draw closer to each other and merge in around 700 million years. This event will create a dazzling supernova of Type Ia and destroy both stars. Image credit: ESO/L. Calçada

Astronomers using ESO facilities in combination with telescopes in the Canary Islands have identified two surprisingly massive stars at the heart of the planetary nebula Henize 2-428. As they orbit each other the two stars are expected to slowly get closer and closer, and when they merge, about 700 million years from now, they will contain enough material to ignite a vast supernova explosion. The results appeared online in the journal Nature on 9th February 2015.

The team of astronomers, led by Miguel Santander-García (Observatorio Astronómico Nacional, Alcalá de Henares, Spain; Instituto de Ciencia de Materiales de Madrid (CSIC), Madrid, Spain), has discovered a close pair of white dwarf stars — tiny, extremely dense stellar remnants — that have a total mass of about 1.8 times that of the Sun. This is the most massive such pair yet found and when these two stars merge in the future they will create a runaway thermonuclear explosion leading to a Type Ia supernova.

This image of the unusual planetary nebula Henize 2-428 was obtained using ESO’s Very Large Telescope at the Paranal Observatory in Chile. Image credit: ESO

 

 

The team who found this massive pair actually set out to try to solve a different problem. They wanted to find out how some stars produce such strangely shaped and asymmetric nebulae late in their lives. One of the objects they studied was the unusual planetary nebula known as Henize 2-428.

“When we looked at this object’s central star with ESO’s Very Large Telescope, we found not just one but a pair of stars at the heart of this strangely lopsided glowing cloud,” says coauthor Henri Boffin from ESO.
This supports the theory that double central stars may explain the odd shapes of some of these nebulae, but an even more interesting result was to come.
“Further observations made with telescopes in the Canary Islands allowed us to determine the orbit of the two stars and deduce both the masses of the two stars and their separation. This was when the biggest surprise was revealed,” reports Romano Corradi, another of the study’s authors and researcher at the Instituto de Astrofísica de Canarias (Tenerife, IAC).
They found that each of the stars has a mass slightly less than that of the Sun and that they orbit each other every four hours. They are sufficiently close to one another that, according to the Einstein’s theory of general relativity, they will grow closer and closer, spiralling in due to the emission of gravitational waves, before eventually merging into a single star within the next 700 million years.
The resulting star will be so massive that nothing can then prevent it from collapsing in on itself and subsequently exploding as a supernova. “Until now, the formation of supernovae Type Ia by the merging of two white dwarfs was purely theoretical,” explains David Jones, coauthor of the article and ESO Fellow at the time the data were obtained. “The pair of stars in Henize 2-428 is the real thing!”
“It’s an extremely enigmatic system,” concludes Santander-García. “It will have important repercussions for the study of supernovae Type Ia, which are widely used to measure astronomical distances and were key to the discovery that the expansion of the Universe is accelerating due to dark energy”.

Hubble Space Telescope still pushing the frontiers of astronomy

Nearly a quarter of a century after its 1990 launch, the Hubble Space Telescope is still pushing the frontiers of observational astronomy, thanks to the sensitivity of its instruments, the ultra precise way the observatory can be controlled and ingenious new techniques that are allowing astronomers to peer deeper into the cosmos than ever before.

"That's why the Hubble is still so exciting," said Matt Mountain, director of the Space Telescope Science Institute at Johns Hopkins University in Baltimore. "We're learning more and more about how to use it even better and better, whether it's looking for exoplanet atmospheres, measuring dark energy to a precision we never thought possible or using gravitational lenses to push Hubble to look even further back in time."

In recent observations, Hubble has been used to search for dim, difficult-to-detect minor planets beyond the orbit of Pluto, possible candidates for a flyby after theNew Horizons probe streaks past Pluto in 2015. Hubble has monitored Jupiter's Great Red Spot, which appears to be shrinking, and a comet -- Siding Spring -- that will make a close flyby of Mars in October.

But it's Hubble's ability to capture light from galaxies shining when the universe was a fraction of its present age that continues to intrigue scientists and the public alike, providing a glimpse into the depths of cosmic history.

To many astronomers, one of Hubble's most mind-boggling observations was a 1995 time exposure of an apparently empty region of space. The resulting "Hubble Deep Field" image, built up over 10 days, revealed thousands of previously unseen galaxies sprinkled like colored jewels on black velvet.

Similar images using newer, more sensitive instruments have revealed a universe populated by uncounted galaxies and fragments of galaxies that somehow began assembling shortly after the big bang birth of the cosmos 13.7 billion years ago.

Now, 20 years after the original Deep Field, Hubble is making another series of long-exposure photographs known as "Frontier Fields." But this time around,Hubble is using the titanic gravity of galaxies and dark matter in nearby clusters to magnify images of even more remote -- and thus younger -- galaxies in the far background.

The result, astronomers hope, will be a glimpse of the universe when it was only 400 million years old, the age when stars and galaxies first began shining as the infant universe expanded and cooled.

NASA's $8 billion James Webb Space Telescope, scheduled for launch in 2018, is optimized to directly image that early epoch in the infrared region of the spectrum, but Hubble's gravity-assist Frontier Fields may provide a tantalizing preview of what's to come.

"Gravity bends light, that was Einstein's discovery, general relativity, and that cluster of galaxies and dark matter can actually behave like a lens and actually magnify objects behind it in the very distant universe," Mountain said in an interview with CBS News. "That allows Hubble to see things even farther away than it could normally."

The resulting gravitationally magnified images are distorted and smeared into arcs "but if you understand the lens, you can recreate the actual shape back where you're going," Mountain said. "Because of our experience over the last few years, we've worked out how to calculate the prescription of the lens so when we see one of these objects we know now how far away it is and how bright it is, which we wouldn't have known before."

How far away is far? And how old is old?

"It's increasing Hubble's ability to go back in time, in very specific areas, back to about 400 million years after the big bang," Mountain said. "That's the incredible thing, that we've managed to calibrate the prescription of these gravitational lenses and now we can use them as tools. Four or five years ago, that wasn't possible."

Closer to home, both in time and space, the hunt for planets orbiting other stars is one of the hottest fields in astronomy, thanks in large part to NASA's Kepler space telescope, a 50-megapixel camera that has discovered thousands of exoplanet candidates.

Mountain said Hubble is using a new technique to study starlight passing through the atmosphere of a confirmed exoplanet as it moves in front of its parent star to measure at least some of its chemical constituents. The trick is being able to separate out the light passing through an atmosphere from the total output of the vastly brighter star.

• Hubble telescope marks another milestone in space

Simply pointing Hubble at a nearby target star will not work because the starlight will saturate the camera's CCD detector, resulting in a blob-like image that cannot be studied with the required precision.

"The problem here is we have to look at very bright stars, and Hubble is very sensitive," Mountain said. "It basically smears the light over the whole camera. It's a bit like when you've got a digital camera and you look at a street lamp by accident at night and you get a streak across your camera. That's the problem Hubble has when it looks at bright stars.

"So the guys here came up with this really cunning idea. Because Hubble can point so accurately, we actually (move the telescope and) drift the star down the camera all the time so you're producing a very straight, linear streak, but it smears the light over the whole CDD and it doesn't saturate."

The resulting streaks can be precisely measured and subtle changes teased out of the data.

"They found a way to very accurately move the telescope while we took the exposure so the light got spread out in these columns and it didn't saturate the camera," Mountain said. "But because we collect all the light over the exposure, we sum up those streaks and we can see those very, very small differences and actually see for the very first time even fainter planets than we could see before."

So far, Hubble has been able to use the technique with a handful of Jupiter-class planets, but Mountain said he is confident researchers eventually will be able to look for signs of water vapor in Neptune-size worlds as observations improve.

Hunting for bigger game, Nobel Laureate Adam Riess, who earlier used Hubble to help confirm the existence of dark energy and its role in speeding up the expansion of the universe, figured out a way to use the streak-exposure technique to improve cosmic distance measurements by a factor of 10.

He came up with the idea while swimming laps in a Baltimore pool, Mountain said. "He thought, oh my God, I could use this technique to help me with my dark energy research."

To directly measure the distance to a star, it must be close enough to Earth that it shifts position when viewed from one side of Earth's orbit and the other. Hold a finger up at arm's length and look at it with one eye and then the other. The finger will change position slightly due to this parallax effect.

Because the 186-million-mile diameter of Earth's orbit is known, astronomers only need to measure the angular shift of a distant star to calculate how far away it must be. But given the scale of the galaxy, even a 186-million-mile baseline means exceedingly small angles. To directly measure the distance to the nearest star, for example, astronomers had to discern angles equivalent to the width of a dime two miles away.

That star, Alpha Centauri, is just 4 light years from Earth. The disk of the Milky Way spans 100,000 light years and millions to billions of light years separate galaxies.

To extend the distance ladder across the gulfs separating galaxies, astronomers use Cepheid variables, stars that pulsate in a predictable manner and have a known intrinsic brightness. By measuring the apparent brightness of a Cepheid in a distant galaxy, and comparing it to the brightness of a Cepheid a known distance from Earth, astronomers can indirectly calculate the distance to that galaxy.

The key is first directly measuring the parallax of a Cepheid in the Milky Way to calibrate the cosmic distance ladder.

Up to this point, direct measurements of stellar distances using parallax extended a few hundred light years. Using the streak-exposure technique, Riess and co-worker Stefano Casertano were able to directly measure the distance to a Cepheid variable star some 7,500 light years out.

"Inside our own galaxy, instead of just looking at very local objects, we can look very far out," Mountain said. "He has managed to change the measurement precision of the universe from 10 percent, he thinks, down to 2 to 3 percent. Why is that important? Well, it's all about dark energy."

A more accurate distance scale allows a more precise characterization of dark energy's effects on the universe at different times in its evolution, shedding light on how the cosmic expansion is changing and how that plays into the ultimate fate of the universe.

Other spacecraft now in development will probe that new frontier in great detail, but Hubble is helping fill in the blanks today by "using its stability and being very smart with new math and new techniques," Mountain said. "So suddenly we've given Hubble a new ability to measure things 10 times more accurately than it could do before."

Rosetta Closing in on Comet 67P/Churyumov-Gerasimenko after Decade Long Chase

ESA’s Rosetta Spacecraft nears final approach to Comet 67P/Churyumov-Gerasimenko in late July 2014. This collage of imagery from Rosetta combines Navcam camera images at right taken nearing final approach from July 25 to July 31, 2014, with OSIRIS wide angle camera image at left of comet’s coma on July 25 from a distance of around 3000 km. On July 31 Rosetta had approached to within 1327 km. Images to scale and contrast enhanced to show further detail. Credit: ESA/Rosetta/NAVCAM/OSIRIS/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Collage/Processing: Marco Di Lorenzo/Ken Kremer

The European Space Agency’s (ESA) Rosetta spacecraft is at last rapidly closing in on its target destination, Comet 67P/Churyumov-Gerasimenko, after a decade long chase of 6.4 billion kilometers through interplanetary space. See imagery above and below.

As of today, Friday, August 1, ESA reports that Rosetta has approached the ‘rubber ducky looking’ comet to within a distance of less than 1153 kilometers. That distance narrows with each passing moment as the speeding robotic probe moves closer and closer to the comet while looping around the sun at about 55,000 kilometers per hour (kph).

Rosetta is now just 5 days away from becoming Earth’s first probe ever to rendezvous and enter orbit around a comet.

See above our image collage of Rosetta nearing final approach with the spacecrafts most recent daily Navcam camera images, all taken within the past week starting on July 25 and including up to the most recently release image snapped on July 31. The navcam images are all to scale to give the sense of the spacecraft approaching the comet and revealing ever greater detail as it grows in apparent size in the cameras field of view.

The highest resolution navcam image yet of the two lobed comet – merged at a bright band – was taken on July 31 from a distance of 1327 kilometers and published within the past few hours by ESA today, Aug 1. It shows the best view yet of the surface features of the mysterious bright necked wanderer composed of primordial ice, rock, dust and more.

 The Navcam collage is combined with an OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) wide angle camera view of the comet and its asymmetric coma of ice and dust snapped on July 25 from a distance of around 3000 km, and with an exposure time of 300 seconds. The OSIRIS image covers an area of about 150 x 150 km (90 mi x 90 mi). The images have been contrast enhanced to bring out more detail.

Scientists speculate that the comets bright neck region could be caused by differences in material or grain size or topological effects.

Rosetta’s history making orbital feat is slated for Aug. 6 following the final short duration orbit insertion burns on Aug. 3 and Aug. 6 to place Rosetta into orbit at an altitude of about 100 kilometers (62 miles) where it will study and map the 4 kilometer wide comet for some 17 months.

The comet rotates around once every 12.7 hours.

The coma of Rosetta’s target comet as seen with the OSIRIS wide-angle camera. The image spans 150 km and was taken on 25 July 2014 with an exposure time of 330 seconds. The greyscale relates to the particle density in the coma, with highest density close to the nucleus, becoming more diffuse further away. The hazy circular structure on the right is an artefact. The nucleus is also overexposured. The specks and the streaks in the background are attributed to background stars and cosmic rays. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Crop from the 31 July processed image of comet 67P/Churyumov-Gerasimenko, to focus on the comet nucleus. Credits: ESA/Rosetta/NAVCAM

“If any glitches in space or on ground had delayed the most recent burns, orbital mechanics dictate that we’d only have had a matter of a few days to fix the problem, re-plan the burn and carry it out, otherwise we run the risk of missing the comet,” says Trevor Morley, a flight dynamics specialist at ESOC.

In November 2014 the Rosetta mothership will deploy the Philae science lander for the first ever attempt to land on a comet’s nucleus using harpoons to anchor itself to the surface.

As Rosetta edges closer on its final lap, engineers at mission control at the European Space Operations Centre (ESOC), in Darmstadt, Germany have commanded the probes navigation camera (navcam) to capture daily images while the other science instruments also collect measurements analyzing the comets physical characteristics and chemical composition in detail.

The probe has already discovered that the comet’s surface temperature is surprisingly warm at –70ºC, which is some 20–30ºC warmer than predicted. This indicates the surface is too hot to be covered in ice and must instead have a dark, dusty crust, says ESA.

Comet 67P/Churyumov-Gerasimenko is a short period comet some 555 million kilometres from the Sun at this time, about three times further away than Earth and located between the orbits of Jupiter and Mars.

You can watch the Aug. 6 orbital arrival live via a livestream transmission from ESA’s spacecraft operations centre in Darmstadt, Germany.

While you were reading this the gap between the comet and Rosetta closed to less than 1000 kilometers!

ESA’s Rosetta Spacecraft nears final approach to Comet 67P/Churyumov-Gerasimenko in late July 2014. This image collage from Rosetta combines Navcam camera images taken nearing final approach from July 25 (3000 km distant) to July 31, 2014 (1327 km distant). Top row shows images as seen by spacecraft. Bottom row shows images rotated to same orientation. Images to scale and contrast enhanced to show further detail. Credit: ESA/Rosetta/NAVCAM. Collage/Processing: Marco Di Lorenzo/Ken Kremer

Controversial clues of two 'Goldilocks planets' that might support life are proven false

Mysteries about controversial signals coming from a dwarf star considered to be a prime target in the search for extraterrestrial life now have been solved in research led by scientists at Penn State University. The scientists have proven, for the first time, that some of the signals, which were suspected to be coming from two planets orbiting the star at a distance where liquid water could potentially exist, actually are coming from events inside the star itself, not from so-called "Goldilocks planets" where conditions are just right for supporting life. The study is published by the journal Science in its early online Science Express edition on July 3, 2014, and also in a later print edition of the journal. This image shows the location of the three planets remaining in 2014 after a series of studies since 2004. Research published in 2014, led by Penn State astronomers, shows that two of the signals previously attributed to planets in the habitable zone are actually created by activity within the star itself. The outer (green) planet shown in a companion image dated 2010 also is believed not to exist, based on work by other researchers since 2010. Blue indicates candidate planets in the habitable zone where conditions might be able to support life, orange indicates detections in the too-hot region that is too close to the star.

Mysteries about controversial signals coming from a dwarf star considered to be a prime target in the search for extraterrestrial life now have been solved in research led by scientists at Penn State University. The scientists have proven, for the first time, that some of the signals, which were suspected to be coming from two planets orbiting the star at a distance where liquid water could potentially exist, actually are coming from events inside the star itself, not from so-called "Goldilocks planets" where conditions are just right for supporting life.

The study will be published by the journal Science in its online Science Express issue on July 3, 2014 and in a future print edition of the journal.

"This result is exciting because it explains, for the first time, all the previous and somewhat conflicting observations of the intriguing dwarf star Gliese 581, a faint star with less mass than our Sun that is just 20 light years from Earth," said lead author Paul Robertson, a postdoctoral fellow at Penn State who is affiliated with Penn State's Center for Exoplanets and Habitable Worlds. As a result of this research, the planets now confirmed to be orbiting this dwarf star total exactly three.

"We also have proven that some of the other controversial signals are not coming from two additional proposed Goldilocks planets in the star's habitable zone, but instead are coming from activity within the star itself," said Suvrath Mahadevan, an assistant professor of astronomy and astrophysics at Penn State and a coauthor of the research paper. None of the three remaining planets, whose existence the research confirms, are solidly inside this star system's habitable zone, where liquid water could exist on a rocky planet like Earth.

Astronomers search for exoplanets by measuring shifts in the pattern of a star's spectrum -- the different wavelengths of radiation that it emits as light. These "Doppler shifts" can result from subtle changes in the star's velocity caused by the gravitational tugs of orbiting planets. But Doppler shifts of a star's "absorption lines" also can result from magnetic events like sunspots originating within the star itself -- giving false clues of a planet that does not actually exist. "In the search for low-mass planets," Mahadevan said, "accounting for the subtle signature of a magnetics events in the star is as important as obtaining the highest possible Doppler precision."

The research team made its discovery by analyzing Doppler shifts in existing spectroscopic observations of the star Gliese 581 obtained with the ESO HARPS and Keck HIRES spectrographs. The Doppler shifts that the scientists focused on were the ones most sensitive to magnetic activity. Using careful analyses and techniques, they boosted the signals of the three innermost planets around the star, but "the signals attributed to the existence of the two controversial planets disappeared, becoming indistinguishable from measurement noise," Mahadevan said. "The disappearance of these two signals after correcting for the star's activity indicates that these signals in the original data must have been produced by the activity and rotation of the star itself, not by the presence of these two suspected planets.

"Our improved detection of the real planets in this system gives us confidence that we are now beginning to sufficiently eliminate Doppler signals from stellar activity to discover new, habitable exoplanets, even when they are hidden beneath stellar noise, said Robertson. "While it is unfortunate to find that two such promising planets do not exist, we feel that the results of this study will ultimately lead to more Earth-like planets."

Older stars such as Gliese 581, an "M dwarf" star in the constellation Libra about one-third the mass of our Sun, have until now been considered highly attractive targets in the search for extraterrestrial life because they are generally less active and so are better targets for Doppler observations. "The new result from our research highlights a source of astrophysical noise even with old M dwarfs because the harmonics of the star's rotation can be in the same range as that of its habitable zone, raising the risk of false detections of nonexistent planets," Mahadevan said. "Higher-precision analysis for discovering Earth-like planets using spectrographs will be increasingly more necessary as next-generation spectrographs with the higher Doppler precision needed for detecting important subtle signatures come on line this decade -- like the Habitable Zone Planet Finder (HPF) that our team now is developing at Penn State."

In addition to Mahadevan and Robertson, other coauthors of the research include Penn State Graduate Student Arpita Roy and McDonald Observatory Research Scientist Michael Endl at the University of Texas. Penn State coauthors have affiliations with the Center for Exoplanets and Habitable Worlds and with the Astrobiology Research Consortium, both at Penn State.