ALMA pinpoints Pluto to help guide NASA's New Horizons spacecraft

The cold surface of Pluto and its largest moon Charon as seen with ALMA on July 15, 2014. 

Credit: NRAO/AUI/NSF

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) are making high-precision measurements of Pluto's location and orbit around the Sun to help NASA's New Horizons spacecraft accurately home in on its target when it nears Pluto and its five known moons in July 2015.

Though observed for decades with ever-larger optical telescopes on Earth and in space, astronomers are still working out Pluto's exact position and path around our Solar System.

ALMA - The Atacama Array

This lingering uncertainty is due to Pluto's extreme distance from the Sun (approximately 40 times farther out than the Earth) and the fact that we have been studying it for only about one-third of its orbit.

Pluto was discovered in 1930 and takes 248 years to complete one revolution around the Sun.

"With these limited observational data, our knowledge of Pluto's position could be wrong by several thousand kilometers, which compromises our ability to calculate efficient targeting maneuvers for the New Horizons spacecraft," said New Horizons Project Scientist Hal Weaver, from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

NASA's New Horizons spacecraft

The New Horizons team made use of the ALMA positioning data, together with newly analyzed visible light measurements stretching back to Pluto's discovery, to determine how to perform the first such scheduled course correction for targeting, known as a Trajectory Correction Maneuver (TCM), in July.

This maneuver helped ensure that New Horizons uses the minimum fuel to reach Pluto, saving as much as possible for a potential extended mission to explore Kuiper Belt objects after the Pluto system flyby is complete.

Animated image of ALMA data showing the motion of the moon Charon around the icy dwarf planet Pluto. 

Credit: B. Saxton (NRAO/AUI/NSF)

To prepare for this first TCM, astronomers needed to pinpoint Pluto's position using the most distant and most stable reference points possible.

Finding such a reference point to accurately calculate trajectories of such small objects at such vast distances is incredibly challenging.

Normally, stars at great distances are used by optical telescopes for astrometry (the positioning of things on the sky) since they change position only slightly over many years.

For New Horizons, however, even more precise measurements were necessary to ensure its encounter with Pluto would be as on-target as possible.

The most distant and most apparently stable objects in the Universe are quasars, galaxies more than 10 billion light-years away.

Though quasars appear very dim to optical telescopes, they are incredibly bright at radio wavelengths, particularly the millimeter wavelengths that ALMA can see.

Ed Fomalont

"The ALMA astrometry used a bright quasar named J1911-2006 with the goal to cut in half the uncertainty of Pluto's position," said Ed Fomalont, an astronomer with the National Radio Astronomy Observatory in Charlottesville, Virginia, and currently assigned to ALMA's Operations Support Facility in Chile.

ALMA was able to study Pluto and its largest moon Charon by picking up the radio emission from their cold surfaces, which are about 43 degrees Kelvin (-230 degrees Celsius).

The team first observed these two icy worlds in November 2013, and then three more times in 2014, once in April and twice in July. Additional observations are scheduled for October 2014.

"By taking multiple observations at different dates, we allow Earth to move along its orbit, offering different vantage points in relation to the Sun," said Fomalont.

"Astronomers can then better determine Pluto's distance and orbit." This astronomical technique is called measuring Pluto's parallax.

"We are very excited about the state-of-the-art capabilities that ALMA brings to bear to help us better target our historic exploration of the Pluto system," said New Horizons Principal Investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado.

"We thank the entire ALMA team for their support and for the beautiful data they are gathering for New Horizons."

ESA ESO ALMA Image: ALMA pinpoints early galaxies at record speed

This video zooms in on some of the galaxies. The large red blobs are the earlier APEX observations and the much sharper views are from ALMA. 

Whereas the APEX images were not sharp enough to identify the emitting galaxies unambiguously the much sharper ALMA images can pin down the emitting galaxies much more precisely. 

The ALMA and APEX observations, at submillimetre wavelengths, are overlaid on an infrared view of the region as seen by the IRAC camera on the Spitzer Space Telescope (coloured blue). 

Credit: ALMA (ESO/NAOJ/NRAO), APEX (MPIfR/ESO/OSO), J. Hodge et al., A. Weiss et al., NASA Spitzer Science Center.

A team of astronomers has used ALMA (the Atacama Large Millimeter/submillimeter Array) to pinpoint the locations of over 100 of the most fertile star-forming galaxies in the early Universe. 

This image shows close-ups of a selection of these galaxies. 

The ALMA observations, at submillimetre wavelengths, are shown in orange/red and are overlaid on an infrared view of the region as seen by the IRAC camera on the Spitzer Space Telescope. 

The best map so far of these distant dusty galaxies was made using the Atacama Pathfinder Experiment (APEX), but the observations were not sharp enough to unambiguously identify these galaxies in images at other wavelengths. 

ALMA needed just two minutes per galaxy to pinpoint each one within a comparatively tiny region 200 times smaller than the broad APEX blobs, and with three times the sensitivity. 

Credit: ALMA (ESO/NAOJ/NRAO), APEX (MPIfR/ESO/OSO), J. Hodge et al., A. Weiss et al., NASA Spitzer Science Center 

A team of astronomers has used the new ALMA (Atacama Large Millimeter/submillimeter Array) telescope to pinpoint the locations of over 100 of the most fertile star-forming galaxies in the early Universe.

ALMA is so powerful that, in just a few hours, it captured as many observations of these galaxies as have been made by all similar telescopes worldwide over a span of more than a decade.

The most fertile bursts of star birth in the early Universe took place in distant galaxies containing lots of cosmic dust.

These galaxies are of key importance to our understanding of galaxy formation and evolution over the history of the Universe, but the dust obscures them and makes them difficult to identify with visible-light telescopes.

To pick them out, astronomers must use telescopes that observe light at longer wavelengths, around one millimetre, such as ALMA.

Jacqueline Hodge

"Astronomers have waited for data like this for over a decade. ALMA is so powerful that it has revolutionised the way that we can observe these galaxies, even though the telescope was not fully completed at the time of the observations," said Jacqueline Hodge (Max-Planck-Institut fur Astronomie, Germany), lead author of the paper presenting the ALMA observations.

The best map so far of these distant dusty galaxies was made using the ESO-operated Atacama Pathfinder Experiment telescope (APEX).

It surveyed a patch of the sky about the size of the full Moon, and detected 126 such galaxies but, in the APEX images, each burst of star formation appeared as a relatively fuzzy blob, which may be so broad that it covered more than one galaxy in sharper images made at other wavelengths.

Without knowing exactly which of the galaxies are forming the stars, astronomers were hampered in their study of star formation in the early Universe.

NASA Aura Satellite Pinpoints Causes of 2011 Arctic Ozone Hole

Maps of ozone concentrations over the Arctic come from the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite. 

The left image shows March 19, 2010, and the right shows the same date in 2011. 

March 2010 had relatively high ozone, while March 2011 has low levels. 

Credit: NASA/Goddard.

A combination of extreme cold temperatures, man-made chemicals and a stagnant atmosphere were behind what became known as the Arctic ozone hole of 2011, a new NASA study finds.

Even when both poles of the planet undergo ozone losses during the winter, the Arctic's ozone depletion tends to be milder and shorter-lived than the Antarctic's.

This is because the three key ingredients needed for ozone-destroying chemical reactions -chlorine from man-made chlorofluorocarbons (CFCs), frigid temperatures and sunlight- are not usually present in the Arctic at the same time: the northernmost latitudes are generally not cold enough when the sun reappears in the sky in early spring. Still, in 2011, ozone concentrations in the Arctic atmosphere were about 20 percent lower than its late winter average.

The new study shows that, while chlorine in the Arctic stratosphere was the ultimate culprit of the severe ozone loss of winter of 2011, unusually cold and persistent temperatures also spurred ozone destruction.

Furthermore, uncommon atmospheric conditions blocked wind-driven transport of ozone from the tropics, halting the seasonal ozone resupply until April.

"You can safely say that 2011 was very atypical: In over 30 years of satellite records, we hadn't seen any time where it was this cold for this long," said Susan E. Strahan, an atmospheric scientist at NASA Goddard Space Flight Center in Greenbelt, Md., and main author of the new paper, which was recently published in the Journal of Geophysical Research-Atmospheres.

"Arctic ozone levels were possibly the lowest ever recorded, but they were still significantly higher than the Antarctic's," Strahan said.

"There was about half as much ozone loss as in the Antarctic and the ozone levels remained well above 220 Dobson units, which is the threshold for calling the ozone loss a 'hole' in the Antarctic - so the Arctic ozone loss of 2011 didn't constitute an ozone hole."

The majority of ozone depletion in the Arctic happens inside the so-called polar vortex: a region of fast-blowing circular winds that intensify in the fall and isolate the air mass within the vortex, keeping it very cold.

Most years, atmospheric waves knock the vortex to lower latitudes in later winter, where it breaks up. In comparison, the Antarctic vortex is very stable and lasts until the middle of spring. But in 2011, an unusually quiescent atmosphere allowed the Arctic vortex to remain strong for four months, maintaining frigid temperatures even after the sun reappeared in March and promoting the chemical processes that deplete ozone.

The vortex also played another role in the record ozone low.

"Most ozone found in the Arctic is produced in the tropics and is transported to the Arctic," Strahan said. "But if you have a strong vortex, it's like locking the door -- the ozone can't get in."