Using “Charon-light,” Researchers Image Pluto’s Dark Side in Faint Moonlight
NASA’s New Horizons Conducts the First Interstellar Parallax Experiment
For the first time, a spacecraft has sent back pictures of the sky from so far away that some stars appear to be in different positions than we see from Earth.
More than four billion miles from home and speeding toward interstellar space, NASA’s New Horizons has traveled so far that it now has a unique view of the nearest stars. “It’s fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth,” said Alan Stern, New Horizons principal investigator from Southwest Research Institute (SwRI) in Boulder, Colorado. “And that has allowed us to do something that had never been accomplished before — to see the nearest stars visibly displaced on the sky from the positions we see them on Earth.”
On April 22-23, the spacecraft turned its long-range telescopic camera to a pair of the closest stars, Proxima Centauri and Wolf 359, showing just how they appear in different places than we see from Earth. Scientists have long used this “parallax effect” – how a star appears to shift against its background when seen from different locations – to measure distances to stars.
The New Horizons Parallax Program
Since its launch in January 2006, NASA’s New Horizons spacecraft has flown past Jupiter in 2007, Pluto in 2015, and most recently, the Kuiper Belt object Arrokoth in 2019. Speeding through the Kuiper Belt at some 31,000 miles (50,000 kilometers) per hour, it’s on a fast path out of the solar system and toward the Milky Way galaxy.
This spring, New Horizons will be more than 46 times farther from the Sun than the Earth, having traveled more than 5 billion miles (8 billion kilometers) since launch. At this great distance, from New Horizons’ view, the nearest stars will appear to have shifted in position relative to more distant stars, compared to where we see them from Earth. On April 22 and 23, 2020, New Horizons will gather images of two of the nearest stars, Proxima Centauri and Wolf 359, to demonstrate this effect.
New Horizons May Have Solved Planet-Formation Cold Case
Not that long ago, it seemed the glory days of NASA’s New Horizons mission were in the rearview mirror, left behind with its historic Pluto encounter in 2015. Then, early last year, the spacecraft streaked by Arrokoth, a bit of flotsam drifting through the Kuiper Belt—the diffuse ring of primitive icy bodies beyond Neptune, of which Pluto is the largest member. What New Horizons found at Arrokoth—initially reported last year and now reinforced with 10 times more data in three studies published last week in Science—is a critical clue to the greatest cold case in the solar system: the mystery of how planets are born.
“I never expected that our encounter with Arrokoth would be shoulder to shoulder with the Pluto flyby in terms of its importance,” says New Horizons principal investigator and study co-author Alan Stern, a planetary scientist at the Southwest Research Institute. “I didn’t expect to make an earth-shattering discovery about planet formation in the Kuiper Belt, and yet we have. At Arrokoth, we stumbled onto maybe the biggest prize of the entire New Horizons mission.”
The Lyman‐α Sky Background as Observed by New Horizons
Recent observations of interplanetary medium atomic hydrogen Lyman‐α emission in the outer solar system, made with the Alice ultraviolet spectrograph on New Horizons, are presented. The observations include regularly spaced great circle scans of the sky and pointed observations near the downstream and upstream flow directions of interstellar H atoms. The New Horizons Alice data agree very well with the much earlier Voyager UVS results, after these are reduced by a factor of 2.4 in brightness, in accordance with recent reanalyses. In particular, the falloff of interplanetary medium Lyman‐α brightness in the upstream‐looking direction as a function of spacecraft distance from the Sun is well matched by an expected 1/r dependence, but with an added constant brightness of ~40 Rayleighs. This additional brightness is a possible signature of the hydrogen wall at the heliopause or of a more distant background. Ongoing observations are planned at a cadence of roughly twice per year.
2014 MU69
2014 MU69
is real weird
In this animated GIF of Kuiper Belt object Ultima Thule made from two images taken 38 minutes apart, the “Thule” lobe is closest to the New Horizons spacecraft. As Ultima Thule is seen to rotate, hints of the topography can be perceived. The images were taken by the Long-Range Reconnaissance Imager (LORRI) at 4:23 and 5:01 Universal Time on January 1, 2019 from respective ranges of 38,000 miles (61,000 kilometers) and 17,000 miles (28,000 kilometers), with respective original scales of 1017 feet (310 meters) and 459 feet (140 meters) per pixel.
No human has ever flown closer to Pluto than Clyde Tombaugh did in 2015, 18 years after his death. That’s fitting, because he was also the first person to lay eyes on it.
When he first glimpsed Planet X, which would go on to be christened Pluto, Tombaugh was just barely 24 and largely self-taught. A farm kid from Streator, Illinois, Tombaugh had once rigged up a backyard telescope made out of parts from a cream separator and a 1910 Buick. He’d earned a gig at the Lowell Observatory, in Flagstaff, Arizona, on the strength of his independent studies. That’s where he spent months sifting through images of the night sky, looking for changes in the orbits of Uranus and Neptune that could potentially be chalked up to the presence of a planet that hadn’t yet been identified.
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Tombaugh died in 1997. Nearly two decades later, one ounce of his cremated remains journeyed to the outer edge of our solar system inside an aluminum capsule aboard the New Horizons spacecraft. The capsule’s inscription eulogizes Tombaugh as a husband, father, astronomer, teacher, punster, and friend.
‘Everything about this flyby is tougher’: New Horizons just over 100 days from Ultima Thule
On New Year’s Day 2019, the spacecraft will come within 3,500 kilometers of 2014 MU69, an estimated 37-kilometer-wide object the mission team has nicknamed Ultima Thule. The encounter will take place 6.6 billion kilometers from Earth, where it takes more than 6 hours for radio signals traveling at the speed of light to reach NASA’s Deep Space Network.
There will only be one chance for New Horizons to perfectly aim its cameras and science instruments at Ultima Thule as it zips past at 14 kilometers per second, and there may be unforeseen hazards in the spacecraft’s path. Nevertheless, Jim Green, the director of NASA’s planetary science division, is looking forward to the drama.
These are the most accurate natural color images of Pluto (left) and its largest moon, Charon (right), taken by NASA’s New Horizons spacecraft as it approached the Pluto system on July 14, 2015. Each is a single color scan from the New Horizons Multispectral Visible Imaging Camera. The images here are not to scale; with a diameter of 1,473 miles, Pluto is about twice the size of Charon (750 miles).
Writing in Science, an international team of geographers, physicists and planetary scientists have analysed detailed images of the dwarf planet’s surface, captured in July 2015 by NASA’s New Horizons spacecraft.
Those images showed that on the boundary of the Sputnik Planitia ice plain, and pushed up against a major mountain range, there is a series of dunes spread across an area less than 75km across.
Following spatial analysis of the dunes and nearby wind streaks on the planet’s surface, as well as spectral and numerical modelling, scientists believe that sublimation (which converts solid nitrogen directly into a gas) results in sand-sized grains of methane being released into the environment.
These are then transported by Pluto’s moderate winds (which can reach between 30 and 40 kmh), with the border of the ice plain and mountain range providing the perfect location for such regular surface formations to appear.
The scientists also believe the undisturbed morphology of the dunes and their relationship with the underlying glacial ice suggests the features are likely to have been formed within the last 500,000 years, and possibly much more recently.
High-Precision Orbit Fitting and Uncertainty Analysis of (486958) 2014 MU69
NASA’s New Horizons spacecraft will conduct a close flyby of the cold classical Kuiper Belt Object (KBO) designated (486958) 2014 MU69 on January 1, 2019. At a heliocentric distance of 44 AU, “MU69” will be the most distant object ever visited by a spacecraft. To enable this flyby, we have developed an extremely high precision orbit fitting and uncertainty processing pipeline, making maximal use of the Hubble Space Telescope’s Wide Field Camera 3 (WFC3) and pre-release versions of the ESA Gaia Data Release 2 (DR2) catalog. This pipeline also enabled successful predictions of a stellar occultation by MU69 in July 2017. We describe how we process the WFC3 images to match the Gaia DR2 catalog, extract positional uncertainties for this extremely faint target (typically 140 photons per WFC3 exposure), and translate those uncertainties into probability distribution functions for MU69 at any given time. We also describe how we use these uncertainties to guide New Horizons, plan stellar occultions of MU69, and derive MU69’s orbital evolution and long-term stability.
New Horizons Captures Record-Breaking Images in the Kuiper Belt
The routine calibration frame of the “Wishing Well” galactic open star cluster, made by the Long Range Reconnaissance Imager (LORRI) on Dec. 5, was taken when New Horizons was 3.79 billion miles (6.12 billion kilometers, or 40.9 astronomical units) from Earth – making it, for a time, the farthest image ever made from Earth.
New Horizons was even farther from home than NASA’s Voyager 1 when it captured the famous “Pale Blue Dot” image of Earth. That picture was part of a composite of 60 images looking back at the solar system, on Feb. 14, 1990, when Voyager was 3.75 billion miles (6.06 billion kilometers, or about 40.5 astronomical units [AU]) from Earth. Voyager 1’s cameras were turned off shortly after that portrait, leaving its distance record unchallenged for more than 27 years.
LORRI broke its own record just two hours later with images of Kuiper Belt objects 2012 HZ84 and 2012 HE85 – further demonstrating how nothing stands still when you’re covering more than 700,000 miles (1.1 million kilometers) of space each day.
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