The Kuiper Belt, or the Edgeworth-Kuiper Belt, is home to ancient rocks. Kuiper Belt Objects, or KBOs, are remnants of the early planet-formation days of our Solar System. Small KBOs, in the 1 km. diameter range, have been theorized about for decades, but nobody’s every found one.
Since it made its historic flyby of Pluto in July of 2015, the New Horizons mission has been venturing farther into the outer Solar System. With the spacecraft still healthy and its system in working order, the mission was extended to include the exploration of additional Kuiper Belt Objects (KBOs). The first target for this part of its mission is the KBO known as 2014 MU69, which New Horizons is currently making its way towards.
In the past, NASA believed this object was a spherical chunk of ice and rock measuring 18–41 km (10–30 mi) in diameter. However, a more recent occultation observation has led the New Horizon‘s team to conclude that MU69 may actually be a large object with a chunk taken out of it (an “extreme prolate spheroid”) or two objects orbiting very closely together or touching – aka. a close or contact binary.
In 2015, MU69 was identified as one of two potential destinations for New Horizons and was recommended to NASA by the mission science team. It was selected because of the immense opportunities for research it presented. As Alan Stern, the Principle Investigator (PI) for the New Horizons mission at the Southwest Research Institute (SwRI), indicated at the time:
“2014 MU69 is a great choice because it is just the kind of ancient KBO, formed where it orbits now, that the Decadal Survey desired us to fly by. Moreover, this KBO costs less fuel to reach [than other candidate targets], leaving more fuel for the flyby, for ancillary science, and greater fuel reserves to protect against the unforeseen.”
The most recent observation of the KBO took place on July 17th, 2017, when the object passed in front of a star. This provided the New Horizon’s team with an opportunity to measure the resulting dip in the star’s luminosity – aka. an occultation – using a series of telescopes that they had deployed to a remote part of Patagonia, Argentina. These sorts of observations are performed regularly in order to obtain estimates of an asteroid’s size and position.
In the case of MU69’s occulation, the New Horizons team was able to obtain vital data that will help the mission planners to plot the trajectory of their flyby. In addition, the data revealed things about MU69’s size, shape, orbit, and the environment that surrounds it. It was because of this that the team began to question earlier estimates on the object’s size and shape.
Based on their new observations, they are confident that the object is no more than 30 km (20 mi) long, if it is an extreme prolate spheroid. If, however, it is a binary, the two objects that compose it are believed to measure about 15-20 km (9-12 mi) in diameter each. Alan Stern expanded on these new findings in a recent NASA press statement, saying:
“This new finding is simply spectacular. The shape of MU69 is truly provocative, and could mean another first for New Horizons going to a binary object in the Kuiper Belt. I could not be happier with the occultation results, which promise a scientific bonanza for the flyby.”
The recent stellar occulation was the third of three observations conducted for the New Horizons mission. To prepare for the event, the New Horizons team traveled to Argentina and South Africa on June 3rd. On July 10th, a week before the occultation, NASA’s airborne Stratospheric Observatory for Infrared Astronomy (SOFIA) provided support by studying the space around MU69.
Using its 2.5 m (100-inch) telescope, SOFIA was looking for debris that might present a hazard to New Horizons spacecraft as it makes its flyby less than 17 months from now. Last, but certainly not least, the team also relied on data provided by NASA’s Hubble Space Telescope and the ESA’s Gaia satellite to calculate and pinpoint where MU69 would cast its shadow on Earth’s surface.
Thanks to their assistance, the New Horizons team knew exactly where the occultation shadow would be and set up their “fence line” of small, mobile telescopes accordingly. Marc Buie – the New Horizons co-investigator – was responsible for leading the observation campaign. As he explained, the data it yielded will be of great help in the planning the flyby, but also indicated that their could be some surprises in the future:
“These exciting and puzzling results have already been key for our mission planning,” he said, “but also add to the mysteries surrounding this target leading into the New Horizons encounter with MU69, now less than 17 months away.”
The flyby with MU69 is scheduled to take place on Jan. 1st, 2019, and will be the most distant flyby in the history of space exploration. In addition to being 1.6 billion km (1 billion mi) from Pluto, the New Horizons spacecraft will be 6.5 billion km (4 billion mi) from Earth! What’s more, the first-ever study of a KBO is expected to yield some fantastic scientific data, and tell us much about the formation and evolution of our Solar System.
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.
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.
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.
“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.”
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.”
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.