The heart-shaped region of Pluto's surface was formed at least in part by a cataclysmic "splat," scientists say. (Credit: NASA / JHUAPL / SwRI)
The most recognizable feature on Pluto is its “heart,” a relatively bright valentine-shaped area known as Tombaugh Regio. How that heart got started is one of the dwarf planet’s deepest mysteries — but now researchers say they’ve come up with the most likely scenario, involving a primordial collision with a planetary body that was a little more than 400 miles wide.
Astronomers from the University of Bern in Switzerland and the University of Arizona looked for computer simulations that produced dynamical results similar to what’s seen in data from NASA’s New Horizons probe. They found a set of simulations that made for a close match, but also ran counter to previous suggestions that Pluto harbors a deep subsurface ocean. They said their scenario doesn’t depend on the existence of a deep ocean — which could lead scientists to rewrite the history of Pluto’s geological evolution.
An artist's conception shows NASA's New Horizons probe and a Kuiper Belt object called Arrokoth. (Credit: JHUAPL / SwRI)
Nearly eight years after its historic Pluto flyby, NASA’s New Horizons probe is getting ready for another round of observations made from the icy edge of the solar system — and this time, its field of view will range from Uranus and Neptune to the cosmic background far beyond our galaxy.
Scientists on the New Horizons team shared their latest discoveries, and provided a preview of what’s ahead, during this week’s Lunar and Planetary Science Conference in The Woodlands, Texas.
It’s been 17 years since the piano-sized New Horizons spacecraft was launched toward Pluto and the Kuiper Belt, The primary mission hit its peak in 2015 when the probe zoomed past Pluto, but the adventure moved on to a second act that focused on a smaller, two-lobed object called Arrokoth — a name derived from the Powhatan/Algonquin word for “sky.”
Scientists are still sifting through the data from the Pluto flyby, and from the Arrokoth flyby on New Year’s Day of 2019, more than 4 billion miles from the sun.
Left: White boxes indicate Ride Rupes (left) and Coleman Mons (right). Right: Features outlined in yellow. (NASA / JHUAPL / SwRI / SETI Inst.)
Two women pioneers of flight now have places of honor on Pluto, thanks to the International Astronomical Union and the team behind NASA’s New Horizons mission.
The IAU has formally approved naming a huge cliff near the southern tip of Pluto’s heart-shaped Tombaugh Regio after Sally Ride (1951-2012), who became the first American woman in space in 1983.
“Sally loved space exploration,” Tam O’Shaughnessy, Ride’s life partner, said in a NASA news release. “Even after her NASA years, she dreamed of joining a mission to the moon or Mars or Pluto. Sally also loved the debate about whether or not Pluto was a true planet. And she appreciated the new criteria for classifying a planet. After all, how else can a planetary scientist decide? Sally would be over the moon — or Pluto — with the honor of having Ride Rupes named after her.”
Not far from Ride Rupes is Coleman Mons, an ice volcano that’s named after Bessie Coleman (1892-1926) the first African-American woman and first Native American to hold a pilot’s license. She earned her license in France in 1923, at a time when U.S. flight schools didn’t admit women or Black people.
“Sally Ride and Bessie Coleman were separated by generations, but they are forever connected by their great achievements, which opened doors for women and girls around the world,” NASA Administrator Bill Nelson said. “In breaking barriers they motivated so many women to pursue dreams and careers they didn’t think were possible, and their sheer persistence and pursuit of equality inspire people to this day.”
Artwork shows the interstellar object ’Oumuamua as a pancake-shaped disk. (William K. Hartmann / Courtesy of ASU / Michael Belton)
It’s not aliens, but it could be a slimmed-down piece of an alien Pluto.
That’s the claim laid out in a pair of studies about the mysterious interstellar object known as ’Oumuamua, which passed through our solar system in 2017.
The studies, published in the AGU Journal of Geophysical Research: Planets, suggest that the flattened chunk of cosmic material consists primarily of solid nitrogen ice, much like the stuff on Pluto’s surface.
The debate over ’Oumuamua — whose name is derived from the Hawaiian phrase for “messenger from afar” — is still raging years after it zipped around the sun and headed back into the celestial darkness. Based on its trajectory, astronomers were certain it came from far beyond the solar system. But was it an asteroid? A comet? Could it even have been an alien spaceship?
Harvard astronomer Avi Loeb favored the alien hypothesis, due to ’Oumuamua’s weird shape and unusually fast getaway. He doubled down on the idea in “Extraterrestrial,” a book published in January. But the authors of the newly published studies, Arizona State University’s Steven Desch and Alan Jackson, say there’s no need to invoke aliens.
“Everybody is interested in aliens, and it was inevitable that this first object outside the solar system would make people think of aliens,” Desch said in a news release. “But it’s important in science not to jump to conclusions. It took two or three years to figure out a natural explanation — a chunk of nitrogen ice — that matches everything we know about ’Oumuamua. That’s not that long in science, and far too soon to say we had exhausted all natural explanations.”
A composite image from NASA’s New Horizons spacecraft shows enhanced-color views of Pluto at lower right and Charon, its largest moon, at upper left. (NASA / JHUAPL / SwRI Photo)
“I think the solar system literally saved the best for last with Pluto,” New Horizons’ principal investigator, Alan Stern of the Southwest Research Institute, said in his anniversary blog post. “Of course, I’m a little biased — as we all are on New Horizons — but I can’t think of a more beautiful and scientifically richer way to have completed the first era of the reconnaissance of the planets.”
This year marks another, more personal anniversary: It’s been 10 years since the publication of “The Case for Pluto,” my book about the put-upon planet. Back then, the big question was whether Pluto deserved the planet label — and although I argued the case that it does, the clash over classification really isn’t that big of a deal anymore.
You can call Pluto a dwarf planet (my preferred term), a Kuiper Belt object or a “bloog.” (That last term is the one Caltech astronomer and self-described Pluto-killer Mike Brown came up with to make fun of the tiff over terminology.)
But in light of New Horizons’ discoveries, you can never call Pluto uninteresting.
It’s interesting to leaf through the pages of “The Case for Pluto” and size up how the speculation from 2010 matches up with the science as we know it in 2020. In honor of the fifth anniversary of the flyby and the 10th anniversary of the book, here are updates on five of the big questions about Pluto:
Is there liquid water on Pluto? Looks like it. New Horizons’ pictures of tectonic structures and mountains made of water ice, plus an analysis of the dwarf planet’s mass distribution, suggest that there are bodies of liquid water hidden beneath the surface layer of nitrogen ice. What’s more, shifts in the state of that water due to freezing may be what’s driving the creation of new faults in the surface ice.
“If Pluto is an active ocean world, that suggests that the Kuiper Belt may be filled with other ocean worlds among its dwarf planets, dramatically expanding the number of potentially habitable places in the solar system,” New Horizons team member James Tuttle Keane, a planetary scientist at NASA’s Jet Propulsion Laboratory, said today in a mission recap.
Does Pluto have plains of methane? Sort of. One of Pluto’s best-known features, a light-colored, heart-shaped zone that was named Tombaugh Regio in honor of the dwarf planet’s discoverer, is dominated by a plain known as Sputnik Planitia. The plain is made up of patchy nitrogen-ice glaciers, but New Horizons also detected the presence of frozen methane, carbon monoxide and water (in the form of icebergs).
Will Pluto’s atmosphere freeze out? The latest evidence suggests a freezing trend. Pluto cycles through seasons in the course of its 248-Earth-year orbit, the dwarf planet’s elliptical orbit is currently taking it farther away from the sun. That means the already-chilly planet and its atmosphere will be getting even colder.
At the time of the New Horizons flyby, scientists saw signs that the atmosphere was still holding steady rather than freezing into flecks of ice, probably due to thermal inertia. But this year, a Japanese team reported that the pressure has apparently dropped by more than 20% since 2016. That’s a much more dramatic collapse than expected, and will need to be confirmed (or discounted) by follow-up observations.
Are there ice volcanoes? You bet … not only on Pluto but on its largest moon, Charon. The pictures from New Horizons suggest that slushy “cryolava” has blurped out onto the surfaces of the two worlds through fissures in the surface ice.
Although the flyby went by too quickly to see the actual blurping, scientists spotted large central pits on two Plutonian mountains known as Wright Mons and Piccard Mons that they believe serve as the mouths of ice volcanoes. And in a region on Charon called Vulcan Planitia, the New Horizons team saw signs of a huge flow of ammonia-rich water ice.
Is there another Planet X out there? Ask again later. Even when “The Case for Pluto” was written, there was plenty of speculation over whether an undetected planet much bigger than Pluto lurked on the solar system’s edge. Caltech’s Mike Brown and other researchers said anomalies in the orbits of objects in the Kuiper Belt hinted at the presence of what they called Planet Nine.
Years of searching through telescope data haven’t yet turned up hard evidence for Planet Nine’s presence, and some astronomers now speculate that the anomalies associated with the hypothetical planet are due instead to the gravitational influence of a grapefruit-sized black hole. Others suggest it’s just a glitch in the data.
Even if Planet X is crossed out. there’s much more to be discovered on the solar system’s last frontier.
The New Horizons team is still sorting through the data sent back from the last year’s follow-up flyby of a double-lobed Kuiper Belt object known as Arrokoth. A huge compendium of Pluto research, running to more than 1,000 pages in length, is being prepared for publication.
Stern and his colleagues are already working to identify a potential target for New Horizons’ third Kuiper Belt flyby. And they’re talking about sending out an orbiter with powerful sensors to conduct a longer-lasting survey of Pluto and the Kuiper Belt.
“By the time we mark the 10th anniversary of the Pluto flyby in July 2025, such a mission could even be under construction,” Stern wrote today.
Who knows? Maybe a 15th-anniversary edition of “The Case for Pluto” will be in the works as well.
A composite image from NASA’s New Horizons spacecraft shows enhanced-color views of Pluto at lower right and Charon, its largest moon, at upper left. (NASA / JHUAPL / SwRI Photo)
Twelve years after the International Astronomical Union voted in a definition of planethood that reclassified Pluto, the debate goes on.
A newly published study uses the historical record to take aim at the definition’s most controversial clause: the idea that a planet in the solar system has to “clear the neighborhood of its orbit,” so that no other worlds are at a similar orbital distance.
An artist’s conception shows Ultima Thule with the New Horizons probe silhouetted by the sun. (NASA / JHUAPL / SwRI Illustration)
The mission operations team for NASA’s New Horizons probe has awakened the spacecraft from its robotic hibernation, and now it’ll stay awake for its scheduled Jan. 1 flyby of a mysterious object on the solar system’s edge, known as 2014 MU69 or Ultima Thule.
New Horizons has been traveling toward Ultima Thule since its history-making Pluto flyby in 2015. To save on resources, the piano-sized probe has been in hibernation mode since last Dec. 21.
The radio signals confirming New Horizons’ latest wakeup call took more than five and a half hours to flash at the speed of light from the solar system’s frontier to NASA’s Deep Space Network, and onward to mission control at Johns Hopkins University’s Applied Physics Laboratory in Maryland. The good news finally arrived at 2:12 a.m. ET today (11:12 p.m. PT June 4).
These maps, assembled using data from the Ralph spectral imager on NASA’s New Horizons probe, shows the relative concentration of four chemicals on Pluto’s surface. Methane is shown in purple, nitrogen in yellow, carbon monoxide in green, and water ice in blue. (NASA / JHUAPL / SwRI Images)
Did Pluto form like its closer-in brethren in the solar system, or is it the result of an agglomeration of comets from the edge of the solar system? A study published in the journal Icarus makes the case for comets.
To reach that conclusion, Christopher Glein and J. Hunter Waite Jr. of the Southwest Research Institute compared chemical analyses from NASA’s New Horizons mission to Pluto with readings from the European Space Agency’s Rosetta mission to Comet 67P/Churyumov-Gerasimenko.
The result is what’s known as the “giant comet” cosmochemical model of Pluto formation.
The 1991 stamp that served as the rallying cry for the New Horizons Mission to Pluto is “updated” by members of the New Horizons science team on July 14, 2015, the day the spacecraft flew past Pluto. Principal investigator Alan Stern is at far left. (Credit: Bill Ingalls / NASA)
It took nine years for NASA’s New Horizons spacecraft to get to Pluto, and laying the groundwork for that history-making space mission here on Earth took nearly twice as long.
The drama and intrigue surrounding New Horizons during those decades, as chronicled in a new book titled “Chasing New Horizons: Inside the First Mission to Pluto,” might be enough for any planetary scientist. But Alan Stern — the book’s co-author, the mission’s principal investigator and arguably Pluto’s most ardent defender — is ready to do it all again.
Stern doesn’t expect his campaign to send an orbiter to Pluto to face quite as many challenges, now that the world knows so much more about the dwarf planet with a giant heart.
“I hope it’s a more straightforward process,” Stern told GeekWire. “First of all, there are now a lot more people who are interested in going back to Pluto. … Now that we’ve done the flyby, there isn’t a planetary scientist in the world that isn’t impressed.”
Last month, Stern and other New Horizons scientists signed onto a white papercalling for NASA to fund an in-depth study of potential Pluto orbiter missions. That grass-roots approach mirrors how the “Pluto Underground” campaign for New Horizons got started around a restaurant table in Baltimore, back in 1989.
“Chasing New Horizons,” written by Stern and astrobiologist David Grinspoon, traces the twists and turns that led from there to the piano-sized spacecraft’s launch in 2006 and its Pluto flyby in 2015.
Pluto’s first official surface-feature names are marked on this map, compiled from images and data gathered by NASA’s New Horizons spacecraft during its flight past Pluto in 2015. (IAU Map)
Some of the best-known places on Pluto, including the heart-shaped Tombaugh Regio, have finally gone legit. But lots of other places, such as Cthulhu Regio, are still in the dark.
The decision from the IAU’s Working Group for Planetary System Nomenclature comes more than two years after NASA’s New Horizons probe flew past Pluto and gave scientists their first-ever detailed look at the dwarf planet.
