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Brightness of galaxies measured using New Horizons’ data; probe enters hibernation

New Horizons in space

Artist’s impression of NASA’s New Horizons spacecraft, en route to a January 2019 encounter with Kuiper Belt Object 2014 MU69. Image & Caption Credit: NASA / JHU-APL / SwRI

A team of astrophysicists is using images captured by NASA’s New Horizons probe during its nine-and-a-half-year journey to Pluto to measure the brightness of all the galaxies in the universe.

In a study published in the journal Nature Communications, the researchers, led by Michael Zemcov of the Rochester Institute of Technology (RIT), used archival data taken by the probe’s Long Range Reconnaissance Imager (LORRI) to study the Cosmic Optical Background – the light beyond the Milky Way galaxy.

The trajectory of New Horizons through the Solar System.

The trajectory of New Horizons through the Solar System. (Click to enlarge) Image Credit: Nature

The photos, all facing away from the Solar System and outward into the Milky Way, were taken at several times and locations including New Horizons’ 2006 launch, its 2007 Jupiter flyby, and four separate positions between Jupiter and Uranus captured in 2007, 2008, and 2010.

Because these images were taken in the outer Solar System, they enabled the researchers to accurately measure the upper limit of light coming from the cosmic optical background.

This background is difficult to see and measure from Earth because sunlight reflected off interplanetary dust in the inner Solar System interferes with the view, significantly brightening Earth’s atmosphere in relation to that of distant galaxies.

“Determining how much light comes from all the galaxies beyond our own Milky Way galaxy has been a stubborn challenge in observational astrophysics,” explained Zemcov, who is both a professor at RIT’s School of Physics and Astronomy and a member of its Center for Detectors and Future Photon Initiative.

Once scientists have an accurate measurement of the cosmic optical background’s brightness, they can determine the number and locations of stars, better understand the inner workings of galaxies, and even gain insight into the activity of dark matter within those galaxies.

NASA’s first outer Solar System missions, Pioneer 10 and Pioneer 11, took the first measurements of brightness beyond the Milky Way, providing scientists with a benchmark for the cosmic optical background’s brightness.

Although these missions are sent to explore planets, their instruments provide a secondary benefit to astrophysics and could potentially be designed to maximize this use.

“This result shows some of the promise of doing astronomy from the outer Solar System. What we’re seeing is that the optical background is completely consistent with the light from galaxies, and we don’t see a need for a lot of extra brightness; whereas previous measurements from near the Earth need a lot of extra brightness. The study is proof that this kind of measurement is possible from the outer Solar System, and LORRI is capable of doing it,” Zemcov said.

For the research team, the study of LORRI images confirms the instrument is capable of providing accurate measurements of light coming from distant galaxies.

The New Horizons mission has been extended to 2021, with the spacecraft traveling further into the Kuiper Belt. Zemcov hopes to use LORRI data captured in this phase of the mission to refine estimates of the cosmic optical background.

“With a carefully designed survey, we should be able to produce a definitive measurement of the diffuse light in the local universe and a tight constraint on the light from galaxies in the optical wavelengths,” he emphasized.

New Horizons enters hibernation

While its data is being used for purposes beyond those of the mission, the New Horizons probe is taking a long-deserved rest, having been put into hibernation on April 7 for the first time since December 2014, when it was awakened to prepare for the July 2015 Pluto encounter.

New Horizons Full Trajectory – Overhead View

Overhead view of New Horizons’ trajectory. Image Credit: NASA / JHU-APL / SwRI

The spacecraft was awake for two-and-a-half years, or 852 days, which is the longest period since launch, beginning with its approach phase six months before the flyby and continuing through the 16 months it took to return all the data captured during the flyby back to Earth.

It has already conducted distant observations of several Kuiper Belt Objects and dwarf planets and also studied the space environment of the Kuiper Belt.

This time, the probe will remain in hibernation for 157 days before being awakened again on September 11, 2017.

During the hibernation period, mission scientists will develop commands for its January 1, 2019, flyby of KBO 2014 MU69, which will be conducted over a nine-day period.

Two potential flyby altitudes over MU69 are being considered. As scientists learn more about the object’s properties and orbit, one of these will be selected.

“We’re looking forward to taking advantage of the reduced mission operations workload during this hibernation, as well as one early next year, to plan much of the MU69 flyby,” said mission operations manager Alice Bowman.



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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