The New Horizons probe made history in July of 2015, being the first mission to ever conduct a close flyby of Pluto. In so doing, the mission revealed some never-before-seen things about this distant world. This included information about its many surface features, it's atmosphere, magnetic environment, and its system of moons. It also provided images that allowed for the first detailed maps of the planet.
Having completed its rendezvous with Pluto, the probe has since been making its way towards its first encounter with a Kuiper Belt Object (KBO) - known as 2014 MU69. And in the meantime, it has been given a special task to keep it busy. Using archival data from the probe's Long Range Reconnaissance Imager (LORRI), a team of scientists is taking advantage of New Horizon's position to conduct measurements of the Cosmic Optical Background (COB).
The COB is essentially the visible light from other galaxies which shines beyond the edge of the Milky Way. By measuring this light, astronomers are able to learn a great deal about the locations of stars, the size and density of galaxies, and test theories about the structure and formation of the Universe. This is no easy task, mind you, as any measurements conducted from inside the Solar System are subject to interference.
The trajectory of the New Horizons probe, which has taken it past Pluto and into the Kuiper Belt. Credit: NASA/JHUAPL
Whereas Earth-based telescopes experience interference from our atmosphere, space-based telescopes have to contend with the brightness of our Sun. In addition, interplanetary dust (IPD) has the effect of scattering light in the Solar System (known as Zodiacal Light) which can also obscure light coming from distant sources. But a probe like New Horizons, which is well into the outer Solar System, is not subject to such interference.
Hence why a team of researchers from the Rochester Institute of Technology (RIT), John Hopkins University Applied Physics Laboratory (JHUAPL), UC Irvine and UC Berkeley, chose to use its data to measure the COB. Their study, titled "Measurement of the cosmic optical background using the long range reconnaissance imager on New Horizons", was recently published in Nature Communications.
For the sake of this study, the team analyzed LORRI data obtained during NH's cruise phase between Jupiter and Uranus. After using data from four different isolated fields in the sky (captured between 2007 and 2010), the team was able to obtain a statistical upper limit on the optical background's brightness.
The study's lead author, Michael Zevkov, is an assistant professor in RIT's School of Physics and Astronomy and a member of RIT's Center for Detectors and Future Photon Initiative. As he stated in an RIT press release:
"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 that LORRI is capable of doing it."
Measuring the light from the Cosmic Optical Background is a way to test cosmological models that explain how the structure and evolution of the Universe. Credit: 2MASS/Caltech
Their results also showed that earlier measurements conducted by Hubble's Wide Field Planetary Camera 2 were excessively bright (owing to interference). However, their results were consistent with previous measurements that were based on data obtained by the Pioneer 10 and 11 missions. Back in the 1970s, these probes managed to gather data on the Universe while swinging past Jupiter and exploring the outer Solar System.
By showing consistency with these results (and other measurements from over the years), the team demonstrated just how valuable missions like New Horizons are. It is hoped that before it wraps up in 2021, that scientists will have a chance to conduct more measurements of the COB. Considering how rare missions to the outer Solar System are, it is understandable why Zemcov and his colleagues want to take full advantage of this opportunity.
"NASA sends missions to the outer Solar System once a decade or so," he said. "What they send is typically going to planets and the instruments onboard are designed to look at them, not to do astrophysics. Measurements could be designed to optimize this technique while LORRI is still functioning... 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 wavebands."
Artist's concept of the New Horizons spacecraft encountering a Kuiper Belt object, part of an extended mission after the spacecraft's July 2015 Pluto flyby. Credits: NASA/JHUAPL/SwRI
In other mission-related news, New Horizons probe will be taking a nap as it approaches its next destination - 2014 MU69. On Friday, April 7th, at 15:32 EDT, mission controllers at the John Hopkins University APL verified that the probe had entered hibernation. It will remain in this state for the next 157 days, waking up again on September 11th, 2017, as it makes its approach to 2014 MU69.
Originally, the New Horizons mission was scheduled to end after its historic encounter with Pluto. However, the mission was extended shortly thereafter to 2021 so the probe would also be able to make some more historic encounters. If, in the meantime, this probe can also shed new light on the mysteries of the Universe, it will surely be remembered as one of the most groundbreaking missions of all time.
Further Reading: RIT, Nature Communications
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