Science News

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Curiosity readies for dramatic entrance
Mars rover to touch down August 5

By Nadia Drake
Web edition : Tuesday, July 31st, 2012

Editor’s note: This is the first of two articles previewing the Mars Curiosity rover’s upcoming Mars landing. This installment describes the vehicle’s landing on the Red Planet, scheduled for Sunday evening, August 5, Pacific Daylight Time; the next will cover the rover’s science mission. Science News astronomy writer Nadia Drake will be covering the landing live from NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

An enormous robot is about to hit the red dirt of Mars — not too hard, NASA hopes — in search of life-friendly environments, or remnants of them. The Curiosity rover’s off-road adventures will begin only if it survives a daring seven-minute, 125-kilometer plunge through the planet’s carbon dioxide atmosphere.

Scientists on Earth expect to observe the touchdown at 10:30 p.m. Pacific Daylight Time on August 5.

Curiosity, which is the size of a small car, is the newest and largest addition to NASA’s family of robotic planet explorers. Its target on Mars is Gale Crater, 154 kilometers wide and home to a massive peak that scientists call Mount Sharp.

After a nearly nine-month journey, the spacecraft carrying Curiosity will enter Mars’ thin atmosphere going approximately 21,250 kilometers per hour. Seven minutes later, just before the rover sets wheels on the fourth rock from the sun, it had better be going approximately zero.

“The Curiosity landing is the hardest NASA robotic mission ever attempted,” says John Grunsfeld, associate administrator for NASA’s Science Mission Directorate. “This is risky business.”

Rather than being cushioned by interplanetary airbags — as the Spirit and Opportunity rovers were in 2004 — Curiosity’s touchdown involves a “sky crane” maneuver that seems ripped from a James Bond film.

That concept includes a parachute deployment 11 kilometers above the planet, once the atmosphere has slowed the spacecraft to a relatively pokey 1,400 kilometers per hour. At 1.6 kilometers above the surface, while falling at nearly 300 kilometers per hour, the parachute is designed to separate from the rover, leaving the craft folded up like a giant bionic insect underneath what’s called the descent vehicle.

Then the descent vehicle should fire its retro-rockets, slowing the plunge even more and setting the stage for the sky crane maneuver to begin. At 20 meters above the planet’s surface — and now dropping at just 2.7 kilometers per hour — the rover will descend from the mother ship on nylon cables and the still-tethered pair will move slowly toward the surface.

“Is it crazy? Well, not so much,” says NASA’s Doug McCuistion. “Once you understand it, it’s not a crazy concept. It works.”

After the rover has stretched its legs and is safely on the ground, it will sever the umbilical cords, allowing the descent vehicle to fly off and ditch itself in the dust about half a kilometer from the landing site.

During the spacecraft’s entry, descent and landing, NASA’s Mars Odyssey orbiter will act as an interplanetary Internet router, relaying information from the rover to scientists on Earth in near real time. (It takes almost 14 minutes for radio signals to travel between the two planets.)

And there will be video: The one-ton, six-wheeled, nuclear-powered rover will film the descent with a camera on its belly. Scientists hope to release the video soon after landing. “That’s just going to be an awesome video, landing on the surface of Mars,” says project scientist John Grotzinger of Caltech. “We’re going to go swinging out like an amusement park ride, and maybe see the flank of Mount Sharp, and then come back down again and see the ground, and the other side — maybe the crater rim.”

After spending a bit of time making sure that all systems are go, the rover will make tracks, driven by scientists wielding computer commands from nearly 250 million kilometers away. “I’m really envious of the rover drivers,” Grotzinger says. “I always wanted to be a rover driver.”

If the spacecraft comes down safely, team members will begin working in shifts on Mars time, synchronizing their days and nights to match the Martian day, which is roughly 40 minutes longer than an Earth day. It’s like being perpetually jet-lagged. “Every day, you come in to work 40 minutes later,” says Ryan Anderson, a planetary scientist at the U.S. Geological Survey Astrogeology Science Center in Flagstaff, Ariz. “If you started in the morning, several weeks later, you’re starting in the middle of the night.”

For at least 90 days, Curiosity will trundle along during the Martian day while scientists on Earth work the Red Planet’s night shift. “We wake up when the rover is going to sleep and work through the Mars night so that by morning, we can send the rover new commands for the next day,” Anderson says.

Of course, all that assumes Curiosity will land safely. If it doesn’t? “We don’t talk about that much,” Anderson says.

Curiosity, NASA’s newest Mars rover, will search for signs of life-friendly environments on Mars — if it survives the journey to the Martian surface on August 5. The journey’s final step is a maneuver that engineers call the sky crane (illustrated), in which a hovering spacecraft lowers the rover to the reddish soil. Credit: NASA; JPL-Caltech

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BLOG: Mission control before the party
Days before Curiosity's planned Martian landing, Nadia Drake checks out JPL's space central

By Nadia Drake
Web edition : Friday, August 3rd, 2012

Though nearly empty Thursday afternoon, mission control at NASA’s Jet Propulsion Laboratory will be packed with more than 100 people when the Mars rover Curiosity is set to touch down this Sunday, August 5.

But for now, the control room is quiet, illuminated by a dim, soothing blue light. Data and images flash across the enormous screens hanging at the front of the room, which also serves as the nerve center for the Deep Space Network, an array of telescopes tasked with tracking the spacecrafts JPL sends zooming around the solar system.

One of the displays tells the team which of these 24 spacecraft are currently phoning home and where on Earth the call is received. At this moment, the Mars Reconnaissance Orbiter is talking to a telescope near Madrid. The Dawn spacecraft, in orbit around the asteroid Vesta, is listening as an antenna in Canberra, Australia, relays instructions. And Juno, on the way to Jupiter, is phoning in to Goldstone, Calif. “There’s a minimum of five engineers here at all times,” says Jim McClure, the facility’s operations manager. “They’re monitoring the data flow from the spacecraft.”

Atop the oxymoronic clean dirt in the In-Situ Instrument Laboratory are Mars Science Laboratory test conductor James Wang, Curiosity's twin on Earth ... and the rubber chicken, perched on the pile of rocks at back, added to the scene during the testing one of the rover’s imaging instruments. Credit: N. Drake

Staffed 24 hours a day since 1964, the Space Flight Operations Facility — which houses mission control — is now a U.S. historical landmark.

In the next room over is the cruise mission support area, a space lined with rows of computers set in front of a large American flag. Here, engineers are responsible for shooting the Mars Science Laboratory spacecraft toward Gale Crater like a well-aimed, cone-shaped meteorite. “We actually picked it up just a few minutes after it launched from Florida, and have been controlling it from here ever since,” says flight director David Oh.

An hour before landing on Sunday evening, a can of peanuts will be popped open and passed around the room — scientists too, it seems, are superstitious and adhere to decades-old rituals. “It’s always been a lucky charm for us,” Oh says. “I think missions have always seemed to work out better when we had the peanuts there.”

In another building on the JPL campus, a mock Curiosity rover is trundling around atop a seeming paradox: clean dirt, a grayish substance that serves as a stand-in for Mars’ red sands. “It’s actually crystals. Small, crushed crystals,” says Eric Aguilar, systems integration and tech manager for the Mars Science Laboratory. “It doesn’t cause as much dust.”

Here, in the In-Situ Instrument Laboratory, scientists test drive landing strategies and practice rover maneuvers. Years ago, the airbags that cushioned the Mars Exploration Rovers Spirit and Opportunity once filled the room to its ceiling. And later, when Spirit found herself stuck on a rock, scientists rolled out her Earthly twin and began sorting out how to free the rover from hundreds of millions of kilometers away.

Now, the team is getting ready for Curiosity’s surface operations — under the watchful eye of a rubber chicken perched atop a pile of rocks. The chicken moved in while the team was testing the Mars Descent Imager, a camera mounted on the rover’s belly. “We needed something to take an image of,” Aguilar explains. “We like to surprise the operations team as they get the data down and take a look.”

The mission control room at JPL in Pasadena, Calif., will be buzzing on the night of August 5, when the NASA rover Curiosity is set to touch down on Mars. Before the big day, the room’s screens relay information about the status of JPL’s 24 interplanetary spacecraft. Credit: N. Drake

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Today at 6:30 AM Lisbon time the Mars Rover should land.

Fingers crossed.

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Wheels down, Mars rover takes in the view
Curiosity lands safely, begins transmitting images

By Nadia Drake
Web edition : Monday, August 6th, 2012

PASADENA, Calif. — Curiosity is alive and well on Mars.

After a daring, well-documented descent into Gale Crater, NASA’s flagship rover came to rest about 6.5 kilometers from the base of Mount Sharp and 28 kilometers from the crater’s northwest rim.

For the next few weeks, Mars’ newest inhabitant will stay put, easing its many instruments into action while snapping photos of its environs. For now, it appears that Curiosity — and all the instruments aboard — are healthy.

“There’s a lot ahead of us, but so far we are just ecstatic about the performance of the vehicle,” said Jennifer Trosper, Mars Science Laboratory mission manager at JPL.

Though Curiosity won’t be stretching its wheels for a few weeks, the rover and its orbiting cousins are busy supplying scientists back home with pictures of the terrifying, seven-minute journey to the crater floor.


From 6.5 kilometers away, Mount Sharp looms large on Curiosity’s Martian horizon. Eventually, the rover will begin climbing this mountain and reading a history of Mars’ ancient environments in its layers. Credit: NASA, JPL-Caltech

“We’re going to make sure that we’re firing on all cylinders before we blaze out across the plains there,” said project scientist John Grotzinger of Caltech.

On August 6, a camera mounted on the rover’s belly returned a series of thumbnail images taken during the plunge into Gale Crater. Strung together into an animation, the 297 images span the descent, beginning with the spacecraft’s heat shield falling away and ending with billowing dust clouds kicked up during the rover’s retrorocket-powered, sky crane–mediated touchdown. A full-resolution video of the descent is expected in a few weeks, said Mike Malin, principal investigator for the Mars Descent Imager and president and chief scientist at Malin Space Sciences Systems in San Diego.

The belly-cam wasn’t the only instrument taking pictures during the rover’s daring skydive into Gale Crater.

An orbiting eye was also watching. From 340 kilometers away, the HiRISE camera aboard the Mars Reconnaissance Orbiter shot an image that shows the rover parachuting into the crater one minute before touchdown. “This was a great, great shot,” said JPL’s Sarah Milkovich, HiRISE investigation scientist. Also in the image: The spacecraft’s heat shield, falling toward Mars. Capturing the image required wrangling the orbiter into place and aiming the camera toward Curiosity, a maneuver the HiRISE team estimated had a 60 percent chance of succeeding.

Curiosity has also sent postcards from its new home in Gale Crater.

The first photo from the surface arrived late in the California evening on August 5, just after the landing, and shows the rover’s rear wheel in front of a field of gravel, with the crater rim rising in the background. “I think that is the best picture of Mars that I’ve ever seen,” Grotzinger said. He notes that it appears as though Curiosity is parked near the edge of an area where flowing water once swept materials over the crater wall and into the basin. “This [process] is bringing materials in from the rim, which is not our destination,” he said. “But we’re getting a free sample without having to drive over there, potentially.”

A later photo from the front of the rover shows Mount Sharp looming in the distance, a massive pile of sediments the likes of which doesn’t exist anywhere on Earth. Unlike large mountains on Earth, Mount Sharp appears to have formed as water and wind filled in the crater, depositing the layered sediments that created the peak. Then, erosion created a moat-like shape, leaving the mountain protruding from the middle of the crater.

Today, Mount Sharp resembles several places on Earth, but with the story of Mars’ environmental history tucked into its layers and awaiting Curiosity’s eager reading.

Even with Mount Sharp calling from the horizon and tantalizing scientific treats underfoot, the rover’s team will take its time deciding where to send Curiosity first. “Be patient with us, please,” said project manager Pete Theisinger after touchdown. “Because we will be patient with Curiosity.”


NASA’s Mars Reconnaissance Orbiter captured Curiosity parachuting into Gale Crater (box, and inset). At this stage in the descent, Curiosity is about a minute from touchdown. Credit: NASA, JPL-Caltech, Univ. of Arizona

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New fossils hint at ancestral split
African discoveries point to two early species in the human genus

By Bruce Bower
Web edition : Wednesday, August 8th, 2012

Newly discovered face and jaw fossils show that at least two species of the human genus Homo lived alongside each other in East Africa nearly 2 million years ago.

These new finds are a good match for a roughly 2 million-year-old Homo brain case and face excavated in 1972 in the same part of East Africa, reports a team led by anthropologist Meave Leakey of the Turkana Basin Institute in Nairobi, Kenya. Long considered a puzzling exception among early Homo finds, the 1972 discovery features big bones and a flat, upright face and represents a species apart, Leakey and her colleagues conclude in the Aug. 9 Nature.

Until now, researchers have found it difficult to exclude the possibility that the large-faced fossil — known as KNM-ER 1470 — came from a male of the same species as smaller, early Homo finds in East Africa.

“After so many years of questions about the identity of the enigmatic 1470 fossil, the chances that it’s from a separate species have greatly improved with our new discoveries,” says anthropologist and study coauthor Fred Spoor of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

Leakey and her colleagues unearthed the new fossils from 2007 to 2009 along the shore of Kenya’s Lake Turkana. Previously dated volcanic ash layers at the site place the finds at between 1.78 million and 1.95 million years old. Further study is needed before assigning the early Homo fossils to particular species, Spoor says, and it’s unclear whether either species led to Homo erectus or to people today. For now, he proposes only that at least two Homo species inhabited East Africa nearly 2 million years ago.

Anthropologist Bernard Wood of George Washington University in Washington, D.C., suspects that Leakey’s team has found fossil evidence for a new, early Homo species distinct from both the 1470 specimen, which he classes as H. rudolfensis, and other Homo fossils from that time, which he groups under H. habilis. The newly found face fossil, which belonged to a child about 8 years old, mirrors the shape of the adult 1470 face, Wood says. But the nearly complete lower jaw and partial lower jaw that Leakey’s team found fit neither in H. rudolfensis nor in H. habilis, he contends.

Evolutionary scientists disagree about whether early Homo fossils can be grouped even into those two species (SN: 3/1/03, p. 131).

Like Wood, anthropologist Donald Johanson of the Institute of Human Origins at Arizona State University in Tempe regards the new face fossil, from the child, and the 1470 fossil as H. rudolfensis. Homo split into at least three African species, including Homo erectus, by about 1.7 million years ago, Johanson says. His team previously excavated the earliest known Homo fossil, an upper jaw from Hadar, Ethiopia, that dates to 2.4 million years ago.

Even Spoor’s proposal that at least two species inhabited East Africa 2 million years ago goes too far, contends anthropologist Tim White of the University of California, Berkeley. Too few early Homo fossils exist to rule out whether the new finds, and the 1470 specimen, fall within a single species that included substantial skeletal differences across individuals and between sexes, White says.

A nearly 2 million-year-old lower jaw discovered recently in East Africa, along with other new finds, differs substantially from smaller, earlier discoveries of Homo fossils in the region, a new study finds. Credit: Mike Hettwer, courtesy of National Geographic

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Curiosity in Exaggerated Color

This color-enhanced view of NASA's Curiosity rover on the surface of Mars was taken by the High Resolution Imaging Science Experiment (HiRISE) on NASA's Mars Reconnaissance Orbiter as the satellite flew overhead. Colors have been enhanced to show the subtle color variations near the rover, which result from different types of materials.

The descent stage blast pattern around the rover is clearly seen as relatively blue colors (true colors would be more gray).

Curiosity landed within Gale Crater, a portion of which is pictured here. The mountain at the center of the crater, called Mount Sharp, is located out of frame to the southeast. North is up.

This image was acquired at an angle of 30 degrees from straight down, looking west. Another image looking more directly down will be acquired in five days, completing a stereo pair along with this image.

The scale of this image cutout is about 12 inches (31 centimeters) per pixel.

HiRISE is one of six instruments on NASA's Mars Reconnaissance Orbiter. The University of Arizona, Tucson, operates the orbiter's HiRISE camera, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter Project for NASA’s Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, built the spacecraft.

Image credit: NASNASA/JPL-Caltech/University of Arizona

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Supersmall lab-on-a-chip is superfast
Nanowire setup may aid speedy detection of health emergencies

By Rachel Ehrenberg
Web edition : Friday, August 17th, 2012

Looking for a specific protein in a drop of blood is like trying to find a notorious white whale on the seven seas — it takes some time. But a new device quickly filters the ocean of molecules in a blood sample, capturing proteins that may warn of an impending heart attack or out-of-whack insulin levels. Besides detecting potential emergencies, such devices could minimize the fraught days a patient spends waiting for lab results, providing them in mere minutes.

Experiments showed the setup detected various levels of troponin T, a cardiac-regulating protein that can signal an impending heart attack, in less than 10 minutes, researchers from Tel Aviv University report online August 2 in Nano Letters. In the future, people at home who are having chest pains might use the technology to find out quickly whether they need to get to an emergency room, says biomedical chemist Fernando Patolsky.

The sugar-cube–sized lab-on-a-chip consists of two small compartments connected by a thin channel. In the first compartment is a densely packed forest of silicon nanowires coated with antibodies, molecules that latch onto specific proteins. The researchers made these nanowires very rough and full of holes, greatly increasing the surface area for attaching the protein-grabbing antibodies.

“They are so rough and porous we can turn a 1-centimeter-square wafer into a 300-centimeter-square surface,” Patolsky says.

The second compartment also contains silicon nanowires, but these are laid flat and their ends are connected to tiny electrodes. After coating both sets of nanowires with antibodies for the specific protein that the researchers want to catch, a tiny drop of blood (between 50 and 250 microliters) is added to the first compartment.

The thick nanowire forest allows the small proteins in the blood that researchers are looking for to move through and be captured by the antibodies, while blocking out larger things, such as cells, that can clog up the works.

A few minutes after the sample is added, the forest is rinsed with water, and a solution that detaches the target proteins from the antibodies is added. Then this concentrated stream of proteins is sent through the channel to the second compartment. The proteins are snatched up again by the antibodies on the flat nanowires, which changes the amount of electrical current passing through the wires. The researchers read this change in current and can determine how much of the protein in question is present in the blood sample.
“It’s clever,” says biomedical engineer Tarek Fahmy of Yale University. “They are doing separation and concentration on the same chip.”

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Surprising rabies resistance
Amazon villagers survive deadly disease carried by vampire bats

By Stephen Ornes
Web edition : 3:56 pm

Rabies is a terrible way to die. The disease is caused by a virus that spreads through animal bites. Without treatment, it attacks the brain and can cause symptoms like hallucinations, paralysis, fever and severe pain. Untreated, the disease is usually deadly — except to some people in a few Peruvian villages, scientists now report.

“Why these individuals don’t die is very intriguing,” Amy Gilbert told Science News. Gilbert is a disease ecologist, a scientist who studies the relationship between germs and their homes. She works for the Atlanta-based Centers for Disease Control and Prevention. Her new study in the American Journal of Tropical Medicine and Hygiene identified these unusual people who caught the rabies virus and survived without treatment.

The survivors live in a part of the Amazon rain forest populated by vampire bats — known carriers of the rabies virus. In those communities, about 1 in 7 people seem to have developed a natural resistance to the virus.

Each year, some 55,000 people worldwide die from rabies. Gilbert and her colleagues now find that all of the Peruvian villagers who survived rabies reported having been bitten by a vampire bat. Only one person reported having received a rabies vaccination.

All of the survivors came from communities that lacked formal roads. One community is a two-hour boat ride away from the nearest health clinic; the other village is six hours from doctors.

Gilbert says that a vampire bat’s bite is mild compared with that of a dog or raccoon. So perhaps rabid bats transmit less of the virus. How close a bite is to the head may also affect a person’s reaction to the virus.

Studies like this one show that researchers still don’t understand everything about this common disease.

“Rabies used to be a disease we said was 100 percent fatal. It was the most deadly disease of all diseases,” Carol Glaser, an infectious disease doctor with the California Department of Public Health, told Science News. But no disease is known to kill every person it infects. In fact, last year, a few people in the United States survived a bout with rabies.

Gilbert cautions that just because some people can survive rabies, the infection shouldn’t be taken lightly. She recommends that children be immunized regularly in places where vampire bats roam.

Power Words

immunize To make a person or animal immune, or resistant, to infection, typically by a vaccine.

rabies A contagious and fatal viral disease of dogs and other mammals that causes madness and convulsions and is transmissible through saliva to humans.

virus A tiny molecule made of a protein shell enclosing genetic information. A virus can live and multiply only in the living cells of a host organism, such as humans.

vampire bat A small bat that feeds on the blood of mammals or birds using its two sharp incisor teeth and anticoagulant saliva. Vampire bats are found mainly in tropical regions of the Americas.

vaccination A treatment given to produce immunity, or resistance, to a disease.

Vampire bats, like this one, can carry rabies virus and transmit it to humans through bites. Daniel Streicker

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Himalayan melt may be less than thought
Satellite data suggest modest net ice loss

By Allison Bohac
Web edition : 3:59 pm

Rising temperatures in the Himalayas may bring more moderate melting for the region’s glaciers than some previous studies have concluded. Combining six years of topographic measurements gathered by NASA’s Ice, Cloud and land Elevation Satellite with radar data collected aboard the space shuttle Endeavour in 2000, an international team mapped out glacier activity throughout the range. Glaciers are thinning faster in some regions than others, but the researchers believe the range as a whole lost nearly 13 billion metric tons of ice per year between 2003 and 2008. While on-the-ground observations indicate heavier losses, this new figure is more than twice the melting tonnage reported earlier this year by another team using data from NASA’s GRACE satellites. The study also challenges the long-accepted idea that an insulating coat of rocky debris can slow down ice loss: Dirty glaciers like Ngozumpa in Nepal shrank at about the same rate on average as their cleaner neighbors, the researchers note August 23 in Nature.

Debris-blanketed glaciers like Nepal’s Ngozumpa, once thought to be relatively immune to melting, have been found to be shrinking at about the same rate as more exposed ice fields. Credit: Kimberly Casey

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Black hole’s annual feast begins
Astronomers offer explanations for source of light around object with an unusual yearly behavior

By Nadia Drake
Web edition : Friday, August 24th, 2012

BEIJING — A black hole about 290 million light-years away has just begun slurping material from its surroundings, an annual ritual revealed by a periodic brightening in X-ray wavelengths.

“It is picking up again, just today — or last night — which is good,” astronomer Roberto Soria of the International Center for Radio Astronomy Research in Perth, Australia, said August 22 at the 28th General Assembly of the International Astronomical Union. “I was starting to get a bit worried because this cycle was three or four days late.”

The black hole, known as HLX-1, is 10,000 times as massive as the sun and the only known specimen in its weight class. Middleweights like HLX-1, which should be numerous, are intermediate between the supermassive black holes at galactic cores — as massive as billions of suns — and the featherweights with just a few solar masses.

First detected by X-ray telescopes in 2009, HLX-1 has since been spied upon in visible wavelengths by the Hubble Space Telescope and other instruments. Those observations revealed a mysterious, bluish glow surrounding the object, which hovers above the plane of a distant galaxy. Now, scientists are trying to determine where the glow is coming from, how HLX-1 formed, and where the rest of the intermediate-mass black holes are hiding.

The most popular theory so far is that the glow is starlight, produced by a cluster of young, blue stars.

But young stars aren’t the only candidates. A different scenario implicates a debris field, or accretion disk, formed by the black hole's annual feasting on a companion star.

“When the [light] was first discovered, it wasn’t clear whether it was a single star, an accretion disk, or a star cluster,” Soria said. “The issue is still not resolved.”

Soria prefers the accretion disk scenario, in which the light comes from a glowing disk formed by the material stolen from a small, companion star. Because the star’s orbit is elliptical, it comes close enough for HLX-1 to slurp some of the star’s mass about once a year. That material then spirals into the disk, creating a transient brightening. Astronomers see an X-ray brightening around the black hole every 366 days or so, presumably the result of this periodic nibbling.
Though that’s a plausible theory, there are some problems with it, said Sean Farrell, an astronomer at Australia’s Sydney Institute for Astronomy, whose observations produced the young star cluster theory.

“I think there is a disk component. We see it in the X-rays; we see it with other black holes,” he said. “The problem is, it’s not enough on its own. The light we see is too bright to be a single star. We think there has to be a cluster of young stars.”

Observing the system again using the Hubble Space Telescope should help resolve the issue, he said.

This class of black holes consisting entirely of HLX-1 was, until 2009, merely theoretical. What’s confounding is that intermediate mass black holes should be numerous, populating the middle ground between featherweight stellar-mass black holes and the supermassive cosmic drains around which galaxies swirl.

Farrell suggests they’re hard to see because most are invisible, stripped of the stars and gas that telescopes can spy on. He speculates that these middleweights are the remains of collapsed primordial stars. Eventually, some became the centers of dwarf galaxies. Then the dwarf galaxies collided, booting their middleweight seeds into space.

“They’ll be floating around in the halos of galaxies, which is exactly where we see this one,” Farrell said. “There could be hundreds of them in every Milky Way–sized galaxy.”

HLX-1, the only known intermediate-mass black hole (circled), hovers above the plane of a nearby galaxy, as seen in this Hubble Space Telescope image. Astronomers are debating the source of the light coming from the area around the black hole. Credit: NASA, ESA, S. Farrell/Sydney Institute for Astronomy