- Mars Lost an Ocean’s Worth of Water
- A Missing Link in the Family Tree of Cosmic Black Holes
- ALMA Performs Its First Very Long Baseline Observations
- Planet 'Reared' by Four Parent Stars
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Posted: 05 Mar 2015 01:30 PM PST
A primitive ocean on Mars held more water than Earth’s Arctic Ocean, and covered a greater portion of the planet’s surface than the Atlantic Ocean does on Earth, according to new results published today. An international team of scientists used ESO’s Very Large Telescope, along with instruments at the W. M. Keck Observatory and the NASA Infrared Telescope Facility, to monitor the atmosphere of the planet and map out the properties of the water in different parts of Mars’s atmosphere over a six-year period. These new maps are the first of their kind. The results appear online in the journal Science today. About four billion years ago, the young planet would have had enough water to cover its entire surface in a liquid layer about 140 metres deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 kilometres. “Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space,” said Geronimo Villanueva, a scientist working at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the new paper. “With this work, we can better understand the history of water on Mars.”
The new estimate is based on detailed observations of two slightly different forms of water in Mars’s atmosphere. One is the familiar form of water, made with two hydrogen atoms and one oxygen, H2O. The other is HDO, or semi-heavy water, a naturally occurring variation in which one hydrogen atom is replaced by a heavier form, called deuterium.
As the deuterated form is heavier than normal water, it is less easily lost into space through evaporation. So, the greater the water loss from the planet, the greater the ratio of HDO to H2O in the water that remains. In oceans on Earth there are about 3200 molecules of H2O for each HDO molecule.
The researchers distinguished the chemical signatures of the two types of water using ESO’s Very Large Telescope in Chile, along with instruments at the W. M. Keck Observatory and the NASA Infrared Telescope Facility in Hawaii. Although probes on the Martian surface and orbiting the planet can provide much more detailed in situ measurements, they are not suitable for monitoring the properties of the whole Martian atmosphere. This is best done using infrared spectrographs on large telescopes back on Earth. By comparing the ratio of HDO to H2O, scientists can measure by how much the fraction of HDO has increased and thus determine how much water has escaped into space. This in turn allows the amount of water on Mars at earlier times to be estimated.
In the study, the team mapped the distribution of H2O and HDO repeatedly over nearly six Earth years — equal to about three Mars years — producing global snapshots of each, as well as their ratio. The maps reveal seasonal changes and microclimates, even though modern Mars is essentially a desert.
Ulli Kaeufl of ESO, who was responsible for building one of the instruments used in this study and is a co-author of the new paper, adds: "I am again overwhelmed by how much power there is in remote sensing on other planets using astronomical telescopes: we found an ancient ocean more than 100 million kilometres away!"
The team was especially interested in regions near the north and south poles, because the polar ice caps are the planet’s largest known reservoir of water. The water stored there is thought to document the evolution of Mars’s water from the wet Noachian period, which ended about 3.7 billion years ago, to the present.
The new results show that atmospheric water in the near-polar region was enriched in HDO by a factor of seven relative to Earth’s ocean water, implying that water in Mars’s permanent ice caps is enriched eight-fold. Mars must have lost a volume of water 6.5 times larger than the present polar caps to provide such a high level of enrichment. The volume of Mars’s early ocean must have been at least 20 million cubic kilometres.
Based on the surface of Mars today, a likely location for this water would be the Northern Plains, which have long been considered a good candidate because of their low-lying ground. An ancient ocean there would have covered 19% of the planet’s surface — by comparison, the Atlantic Ocean occupies 17% of the Earth’s surface.
“With Mars losing that much water, the planet was very likely wet for a longer period of time than previously thought, suggesting the planet might have been habitable for longer,” said Michael Mumma, a senior scientist at Goddard and the second author on the paper.
It is possible that Mars once had even more water, some of which may have been deposited below the surface. Because the new maps reveal microclimates and changes in the atmospheric water content over time, they may also prove to be useful in the continuing search for underground water.
NASA is studying Mars with a host of spacecraft and rovers under the agency’s Mars Exploration Program, including the Opportunity and Curiosity rovers, Odyssey and Mars Reconnaissance Orbiter spacecraft, and the MAVEN orbiter, which arrived at the Red Planet in September 2014 to study the planet’s upper atmosphere.
In 2016, a Mars lander mission called InSight will launch to take a first look into the deep interior of Mars. The agency also is participating in ESA’s (European Space Agency) 2016 and 2018 ExoMars missions, including providing telecommunication radios to ESA’s 2016 orbiter and a critical element of the astrobiology instrument on the 2018 ExoMars rover. NASA’s next rover, heading to Mars in 2020, will carry instruments to conduct unprecedented science and exploration technology investigations on the Red Planet.
This research was presented in a paper entitled “Strong water isotopic anomalies in the Martian atmosphere: probing current and ancient reservoirs”, by G. VIllanueva et al., to appear online in Science on 5 March 2015.
The team is composed of G.L. Villanueva (NASA Goddard Space Flight Center, Greenbelt, USA; Catholic University of America, Washington, D.C., USA), M.J. Mumma (NASA Goddard Space Flight Center), R.E. Novak (Iona College, New York, USA), H.U. Käufl (ESO, Garching, Germany), P. Hartogh (Max Planck Institute for Solar System Research, Göttingen, Germany), T. Encrenaz (CNRS — Observatoire de Paris-Meudon, Paris, France), A. Tokunaga (University of Hawaii-Manoa, Hawaii, USA), A. Khayat (University of Hawaii-Manoa) and M. D. Smith (NASA Goddard Space Flight Center).
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Posted: 05 Mar 2015 12:55 PM PST
A black hole discovered wandering all by itself inside one of the spiral arms of the galaxy NGC 2276 may present an important clue that would fill the gap in the evolutionary story of black holes. This discovery has been reported recently by a research team which is led by Mar Mezcua from the Harvard Centre for Astrophysics in Boston and includes Andrei Lobanov from the Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn. They identify this elusive black hole, called NGC 2276-3c. The astronomers had to look at it simultaneously at radio waves with the European Very Long Baseline Interferometry Network, or EVN, and in X-rays with NASA’s Chandra Space Observatory. The combination of X-ray and radio data enables the researchers to ‘weigh’ the black hole, which has turned out to be as heavy as about 50,000 Suns. With this mass, it fills a gap between stellar black holes found in our own Galaxy and supermassive black holes residing in centers of most of the massive galaxies. Such intermediate-mass black holes are probably the seeds from which supermassive black holes will form.
The new source is located in a spiral arm of the galaxy NGC 2276, which is separated by about 100 million light years from Earth, in the direction of the constellation Cepheus not too far from the North pole in the sky. Its detection may provide answers to some long-standing questions about how black holes evolve and influence their surroundings.
“In paleontology, the discovery of certain fossils can help scientists fill in the gaps of the dinosaurs,” says Mar Mezcua of the Harvard-Smithsonian Center for Astrophysics, who led the study. “We do the same thing in astronomy, but we often have to ‘dig’ up our discoveries in galaxies that are trillions of miles away.”
The intriguing object appears to be what astronomers call an “intermediate-mass black hole” or IMBH. For many years, scientists have found conclusive evidence for smaller black holes that contain only a few times the mass of the sun. There is also a lot of information about so-called supermassive holes that reside at the center of galaxies and weigh millions or even billions the sun’s mass.
As their name suggests, IMBHs represent a class of black holes that fall in between these two well-established groups. One reason that IMBHs are important is that they could be the seeds from which supermassive black holes formed in the early universe. The discovery in NGC 2276 would represent just the second IMBH that is found outside the center of a galaxy.
“Astronomers have been looking very hard for these medium-sized black holes,” explains co-author Timothy Roberts of the University of Durham in the UK. “There have been hints that they exist, but the IMBHs have been acting like a long-lost relative that isn’t interested in being found.”
To learn about this object, the researchers observed NGC 2276 almost simultaneously in radio waves with the EVN (including MPIfR’s Effelsberg 100m radio telescope) and in X-rays with Chandra. Each telescope provided critical and complementary information about this source. Moreover, both radio and X-ray data were necessary to get an accurate determination of the black hole’s mass, estimated to be about 50,000 times that of the Sun.
“We found that this IMBH has traits similar to both stellar-mass black holes and supermassive black holes” says co-author Andrei Lobanov of MPIfR. “In other words, this object helps tie the whole black hole family together.”
In addition to its size and location, there are several intriguing properties to the IMBH in NGC 2276. The black hole appears to have a powerful jet that extends for up to 2,000 light years, demonstrating the reach this black hole has.
A region about 1,000 light years long next to the jet seems to be missing young stars. This might provide evidence that the jet has cleared out a cavity in the gas, suppressing the formation of new stars. This is an important hint in how IMBHs influence their environment. This jet detection might also show that supermassive black hole seeds in the early universe had a large impact on their surroundings.
“There is an interesting open question”, concludes Mar Mezcua. “We are trying to determine if the black hole in NGC 2276 was formed within the galaxy or if it was created during a merger with a dwarf galaxy in the past.”
The study on NGC 2276-3c was conducted by Mar Mezcua (after completing her PhD at MPIfR’s IMPRS research school in 2011 she was in the Instituto de Astrofisica de Canarias and is now at the Harvard-Smithsonian Center for Astrophysics), Tim Roberts (University of Durham, UK), Andrei Lobanov (MPIfR), and Andrew Sutton (University of Durham). The study appears in the Monthly Notices of the Royal Astronomical Society (MNRAS).
Credit: mpifr-bonn.mpg.de
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Posted: 05 Mar 2015 12:25 PM PST
ALMA, the Atacama Large Millimeter/submillimeter Array, has successfully combined its immense collecting area and sensitivity with that of APEX (Atacama Pathfinder Experiment) to create a new, single instrument through a process known as Very Long Baseline Interferometry (VLBI). “The entire team is immensely gratified at achieving this success on the first VLBI attempt with ALMA. It marks a huge step toward making first images of a black hole with the Event Horizon Telescope," said Shep Doeleman, the principal investigator of the ALMA Phasing Project and assistant director of the Massachusetts Institute of Technology’s Haystack Observatory and astrophysicist at the Smithsonian Astrophysical Observatory.
Larger telescopes can make sharper observations, and interferometry allows multiple telescopes to act like a single telescope as large as the separation — or baseline — between them. In VLBI, data from two independent telescopes are combined to form a virtual telescope that spans the geographic distance between them — potentially up to the diameter of the Earth — yielding extraordinary magnifying power.
An essential intermediate step is to test the technique on a short baseline. On 13 January 2015 ALMA and the nearby APEX telescope simultaneously studied the quasar 0522-364. This distant galaxy was used for this first-of-its-kind observation due to its remarkable brightness at radio wavelengths.
To ensure the telescopes were in sync, ALMA used a newly installed and exquisitely precise atomic clock to time-code the data as it was collected. An accurate time is essential for VLBI because it enables data taken at different geographical locations on different telescopes to be precisely matched and accurately integrated. The analysis of the data, which was recently completed, confirmed that the system was working correctly and that the ALMA atomic clock is precise enough for VLBI.
This first successful observation using VLBI with ALMA used a baseline of 2.1 km, and was an essential proof-of-concept test for the planned Event Horizon Telescope, which eventually will include a global network of millimetre-wavelength telescopes. When fully assembled, the Event Horizon Telescope — with ALMA as the largest and most sensitive site — will form an Earth-size telescope with the magnifying power required to see details at the edge of the supermassive black hole at the centre of the Milky Way.
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Posted: 05 Mar 2015 11:48 AM PST
Growing up as a planet with more than one parent star has its challenges. Though the planets in our solar system circle just one star -- our sun -- other more distant planets, called exoplanets, can be reared in families with two or more stars. Researchers wanting to know more about the complex influences of multiple stars on planets have come up with two new case studies: a planet found to have three parents, and another with four. The discoveries were made using instruments fitted to telescopes at the Palomar Observatory in San Diego: the Robo-AO adaptive optics system, developed by the Inter-University Center for Astronomy and Astrophysics in India and the California Institute of Technology in Pasadena, and the PALM-3000 adaptive optics system, partially funded by NASA and developed by NASA's Jet Propulsion Laboratory in Pasadena, California, and Caltech.
This is only the second time a planet has been identified in a quadruple star system. While the planet was known before, it was thought to have only three stars, not four. The first four-star planet, KIC 4862625, was discovered in 2013 by citizen scientists using public data from NASA's Kepler mission.
The latest discovery suggests that planets in quadruple star systems might be less rare than once thought. In fact, recent research has shown that this type of star system, which usually consists of two pairs of twin stars slowly circling each other at great distances, is itself more common than previously believed.
"About four percent of solar-type stars are in quadruple systems, which is up from previous estimates because observational techniques are steadily improving," said co-author Andrei Tokovinin of the Cerro Tololo Inter-American Observatory in Chile.
The newfound four-star planetary system, called 30 Ari, is located 136 light-years away in the constellation Aries. The system's gaseous planet is enormous, with 10 times the mass of Jupiter, and it orbits its primary star every 335 days. The primary star has a relatively close partner star, which the planet does not orbit. This pair, in turn, is locked in a long-distance orbit with another pair of stars about 1,670 astronomical units away (an astronomical unit is the distance between Earth and the sun). Astronomers think it's highly unlikely that this planet, or any moons that might circle it, could sustain life.
Were it possible to see the skies from this world, the four parent stars would look like one small sun and two very bright stars that would be visible in daylight. One of those stars, if viewed with a large enough telescope, would be revealed to be a binary system, or two stars orbiting each other.
In recent years, dozens of planets with two or three parent stars have been found, including those with "Tatooine" sunsets reminiscent of the Star Wars movies. Finding planets with multiple parents isn't too much of a surprise, considering that binary stars are more common in our galaxy than single stars.
"Star systems come in myriad forms. There can be single stars, binary stars, triple stars, even quintuple star systems," said Lewis Roberts of JPL, lead author of the new findings appearing in the journal Astronomical Journal. "It’s amazing the way nature puts these things together."
Roberts and his colleagues want to understand the effects that multiple parent stars can have on their developing youthful planets. Evidence suggests that stellar companions can influence the fate of planets by changing the planets' orbits and even triggering some to grow more massive. For example, the "hot Jupiters" -- planets around the mass of Jupiter that whip closely around their stars in just days -- might be gently nudged closer to their primary parent star by the gravitational hand of a stellar companion.
In the new study, the researchers describe using the automated Robo-AO system on Palomar Observatory to scan the night skies, searching hundreds of stars each night for signs of stellar companions. They found two candidates hosting exoplanets: the four-star system 30 Ari, and a triple-star planetary system called HD 2638. The findings were confirmed using the higher-resolution PALM-3000 instrument, also at Palomar Observatory.
The new planet with a trio of stars is a hot Jupiter that circles its primary star tightly, completing one lap every three days. Scientists already knew this primary star was locked in a gravitational tango with another star, about 0.7 light-years away, or 44,000 astronomical units. That's relatively far apart for a pair of stellar companions. The latest discovery is of a third star in the system, which orbits the primary star from a distance of 28 astronomical units -- close enough to have influenced the hot Jupiter's development and final orbit.
"This result strengthens the connection between multiple star systems and massive planets," said Roberts.
In the case of Ari 30, the discovery brought the number of known stars in the system from three to four. The fourth star lies at a distance of 23 astronomical units from the planet. While this stellar companion and its planet are closer to each other than those in the HD 2638 system, the newfound star does not appear to have impacted the orbit of the planet. The exact reason for this is uncertain, so the team is planning further observations to better understand the orbit of the star and its complicated family dynamics.
JPL is managed for NASA by the California Institute of Technology in Pasadena.
Credit: NASA
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