Lecture: Unveiling Dwarf Planet Ceres

Flight Over Dwarf Planet Ceres

The dwarf planet Ceres is a complex and active world unlike any other place in the solar system, new research suggests.

Observations by NASA's Ceres-orbiting Dawn spacecraft indicate that "ice volcanos" have erupted on the dwarf planet in the recent past and that Ceres' crust is an odd ice-rock mixture that has never been observed before, scientists reported in a series of six new studies published online today (Sept. 1) in the journal Science.

"When we got to Ceres, we were expecting to be surprised, and we have been in many ways," Dawn principal investigator Chris Russell, a professor of geophysics and space physics at the University of California, Los Angeles (UCLA), told Space.com. [Watch: An Ice Volcano on Ceres]

"Ceres has been active during its history inside; the interior has been changing, evolving, much like the Earth's interior changes with time," added Russell, lead author of one of the new Science papers and co-author on the other five. "It's in the transition between the smaller asteroids and the Earth, in that it changes, and has changed, over the years from the time that the material initially came together."

**NASA's Dawn probe captured this high-resolution image of the Ceres mountain Ahuna Mons. Image width is 19 miles (30 kilometers).**
**Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA**

Eyeing the queen of the asteroid belt

Dawn launched in September 2007 on a $467 million mission to study the two largest objects in the main asteroid belt between Mars and Jupiter — the 330-mile-wide (530 kilometers) protoplanet Vesta and Ceres, which is about 590 miles (950 km) across.

Dawn orbited Vesta from July 2011 through September 2012, when the probe departed for Ceres. The spacecraft arrived at the dwarf planet in March 2015, in the process becoming the first probe ever to orbit two different bodies beyond the Earth-moon system.

Scientists already knew a bit about Vesta, based on analyses of rocks that were blasted off the object long ago and have fallen to Earth as meteorites. Dawn's work confirmed suspicions that Vesta is basically "frozen in time," Russell said.

"It formed early and cooled off rapidly, and has just been a very solid body that was battered by impacts," he said.

Ceres was more mysterious, because no meteorite "family" is associated with the dwarf planet. But Dawn has discovered that Ceres is an altogether different beast than its asteroid belt neighbor, as the six new Science papersshow.

Perspective view of the Ceres mountain Ahuna Mons in false color derived from Dawn’s framing-camera data. The bluish color of the mountain’s flanks probably represents a compositional change. Ahuna Mons is 2.5 miles tall and 10.5 miles wide (4 by 17 kilometers).
**Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA**

An active world

For example, the surface of Ceres is much more diverse and complex than that of Vesta, possessing extensive linear structures, lobed features caused by flowing material and a 2.5-mile-high (4 km) mountain (in addition to numerous craters).

This massif, known as Ahuna Mons, resembles the dome-shaped mountains created by volcanism here on Earth, researchers reported in one of the new studies. And Dawn team members said they think Ahuna Mons was indeed created by a volcano, but one that spewed out cold, molten ice rather than hot, liquid rock.

The researchers — led by Ottaviano Ruesch, of NASA's Goddard Space Flight Center in Greenbelt, Maryland — said they aren't sure exactly what Ceres' "cryomagma" is made of, but they suggested it could be a mix of chlorine salts and water ice.

Furthermore, Ahuna Mons appears to be quite young, the researchers said. Analyses of crater counts suggest that the mountain formed in the last 200 million years or so, study team members said. (Like the rest of the solar system, Ceres itself formed about 4.56 billion years ago.)

In another one of the new studies, a team led by Debra Buczkowski,,of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, identified other dome-shaped features that also appear to be products of cryovolcanism (though not all of it as recent as the activity responsible for Ahuna Mons). Buczkowski and her colleagues also concluded that some of Ceres' linear features likely represent subsurface faults.

Ceres doesn't experience tidal heating; its insides are never churned and heated by another object's powerful gravitational pull, because Ceres never gets close enough to a giant planet. So the energy driving geological activity such as cryovolcanism must come from the dwarf planet's internal heat, Russell said — primarily the heat left over from the object's long-ago formation, with some contribution from radioactive decay processes.

"Ceres is cooling down, but it hasn't cooled down yet," he said.

Ceres is probably similar in this respect to Pluto, another dwarf planet that hasremained geologically active into the recent past. (The powerful ice geysers that blast from the south polar region of the Saturn moon Enceladus, on the other hand, are driven by tidal heating.)

Astronomers know, based on Ceres' measured density, that the dwarf planet harbors a large amount of water. Over the years, there's been some speculation that a subsurface ocean such as the one on Enceladus may exist on Ceres.

If Ceres ever had such an ocean, it's probably gone now, Russell said. But the dwarf planet may still be able to support life as we know it, he added.

"We now know that there is water, and there is enough heat in the interior that that water can be in liquid form," Russell said. "There's certainly water, or brine, that can flow through the system and reach the surface." [Dwarf Planet Ceres' Intriguing Features Seen in New Detail (Video)]

Ceres' odd crust

Before Dawn got to Ceres, most astronomers thought the dwarf planet's crust consists primarily of water ice. But another one of the new Science studies, which is based on a detailed analysis of Ceres' many craters, suggested that's not the case.

Water ice is fairly soft, at least compared to rock. So if Ceres had a primarily icy shell, the dwarf planet's craters would tend to "relax," or flatten out, on relatively short timescales: 10 million to 100 million years or so, the researchers said. But study leader Harald Hiesinger, of the University of Munster in Germany, and his colleagues didn't find the expected relaxation.

Instead, Ceres' crater morphology suggests that the dwarf planet's crust is a strange mix of perhaps 60 percent rock and 40 percent ice, Russell said.

"This is something that we haven't seen before," he said.

"It's a new material to us — something that, if you hit it really hard, it will melt and flow, but you don't have to warm it up to the temperature of lava," Russell added. "We have many, many different areas where the material has flowed across the surface after having been hit by perhaps a meteorite or something of that nature." [Take a Trippy Trip Over Dwarf Planet Ceres (Video)]

NASA's Dawn spacecraft is the first ever to visit two targets in the asteroid belt, Vesta and Ceres. See how NASA's Dawn spacecraft will visit the asteroids Vesta and Ceres in this Space.com infographic.
**Credit: Karl Tate/Space.com**

A thin atmosphere?

Another of the new studies, this one led by Russell, suggested that Ceres may possess a thin atmosphere; such an "exosphere" could explain Dawn's observations of the solar wind interacting with the dwarf planet, the researchers wrote.

One of the other Science papers reported the probable detection of water ice, likely unearthed by an impact or landslide, at the bottom of a crater named Oxo. Another paper concluded that Ceres' surface was likely substantially altered by water at some point in the past, based on the widespread distribution of clay minerals (which only form in water).

These two studies were led by Jean-Philippe Combe (of the Bear Fight Institute in Winthrop, Washington) and Eleonora Ammannito (of UCLA), respectively.

(The new papers don't touch much on Ceres' famous bright spots, which appear to be composed largely of carbonates, Dawn team members recently reported.)

More discoveries to come

Dawn should help astronomers refine their understanding of Ceres even more in the future; NASA recently extended the spacecraft's mission by an additional two years.

For the past eight months or so, Dawn has been studying Ceres from an altitude of just 240 miles (385 km). But on Friday (Sept. 2), the probe will begin spiraling out to a higher orbit, one that lies 910 miles (1,460 km) above the dwarf planet's surface.

The move will allow Dawn to save fuel, NASA officials said. In addition, Dawn should be able to make better targeted observations from the more distant orbit, Russell told Space.com.

During the remainder of the mission, the Dawn team will look hard for changes in Ceres' surface over time, to get a better handle on the dwarf planet's geological activity and processes, Russell said.

The team is particularly interested in better understanding how often material makes it from Ceres' subsurface onto the surface, he added.

"We know that there is liquid inside Ceres," Russell . "Does it come out on a regular basis, or does it just leak out as vapor? Or are there outgassing events?"

A possible outgassing event occurred several years ago on Ceres: In January 2014, researchers reported that Europe's Herschel Space Observatory had detected a transient cloud of water vapor around the dwarf planet. Dawn is not equipped to detect water vapor directly, but the probe may be able to spot a plume by indirect means, Russell said.

The Herschel detection "suggested that there were times when there was more atmosphere than others," he said. "We would love to be able to check that out."

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us@Spacedotcom, Facebook or Google+. Originally published on Space.com.

The Universe - Search for Extraterrestrial Life

The billions of stars in the night sky can give rise to the question, are we alone in the universe? The Search for Extraterrestrial Intelligence (SETI) seeks to answer that question by hunting for signs of advanced civilizations in the cosmos.

The term SETI can be applied in two ways. The first characterizes the quest itself, the search for other advanced lifeforms undertaken by people around the world. The SETI Institute, the second application, leads the charge in the pursuit of broadcasts from life beyond Earth.

The SETI Institute

The largest player in the hunt for advanced life beyond the solar system, the SETI Institute is made up of scientists, engineers, technicians, teachers, and other support staff. In 1988, NASA began funding a strategy to sweep all directions of the sky in the hunt for life. Observations began in 1992, on the 500^th anniversary of Christopher Columbus' arrival in the New World. However, within a year, Congress terminated funding.

The SETI Institute then sought private funding to continue the hunt for advanced life in the universe. Donations from the enthusiastic public have helped continue the hunt for signals from other worlds. According to its website, the Institute has over 100 active projects, spanning astronomy and planetary sciences, chemical evolution, the origin of life and climate change.

Project Phoenix continued the targeted search initially instituted by NASA. The program carefully examined regions around a thousand nearby sun-like stars with the world's largest antennae.

In a joint project with the University of California, Berkeley, the Institute built 42 individual telescopes that function as a single massive instrument. TheAllen Telescope Array, named for benefactor Paul Allen (co-founder of Microsoft), began observations in 2007. According to the SETI Institute, the array should allow scientists to examine as many as 1 million nearby stars in the next two decades.

Hunting for advanced life

Extraterrestrial life can be roughly grouped into two categories. The first is the broad classification of life itself, a process that includes microbial and other simple forms. Without civilization and technology, life cannot produce the advanced signals that travel across the galaxy. However, many scientists continue to investigate atmospheres and other characteristics of worlds both in and out of the solar system as part of the search for life beyond our planet.

The search for extraterrestrial intelligence looks beyond this broad category in an effort to find advanced civilizations. Most SETI searches focus on the hunt for radio or optical signals that can signify highly evolved alien life.

Because life on Earth arose within 100 million years after the planet was habitable, many scientists think that life should evolve on planets with the right characteristics. With billions of stars in the galaxy, each thought to host at least one planet, there are numerous opportunities for life to evolve. The wealth of planets revealed by NASA's Kepler space telescope have produced a slew of potentially habitable worlds for SETI scientists to target.

According to SETI Institute astronomer Seth Shostak, there are three ways to find life on other worlds. The first is to go and look, a process only feasible within the solar system. The second is by studying light from the planet to investigate its atmosphere, currently under way with instruments like NASA's Hubble Space Telescope. The third is to search for signals that could indicate intelligence.

"That's what SETI does," Shostak said in a broadcast.

Most SETI searches focus on radio signals, and most of these hunt for narrow-band signals, radio emissions that cover only a small portion of the radio spectrum. Natural objects blanket the spectrum with signals, so finding a signal that only dominated a small region would be suggestive of an artificial source.

Scientists also focus on optical searches for advanced civilizations. These hunts involve looking for very brief flashes of light that last only nanoseconds.

Messages from other worlds could be deliberately beamed or they could be accidental. Earth has been broadcasting signals since World War II, when radio communications became more common. SETI searches also look for intentional messages transmitted into space. More recently, the SETI hunt has begun to look for communications between two worlds along Earth's line of sight; messages beamed toward a planet or moon in the system couldcontinue on toward Earth.

Whether or not humans would be capable of understanding the message is another story. If a civilization is deliberately beaming a message into space, they may seek to distill it to its simplest form. However, if the message is accidentally broadcast or is a message for another world, it is possible that scientists will never be able to decode it.

According to the SETI Institute, the signal will reveal a few things about the civilization producing it. Scientists will be able to pinpoint its origination, and changes can help determine how the planet is rotating and moving.

"But even though this information is limited, the detection of an alien intelligence will be an enormously big story," the SETI Institute said on its website.

"We'll be aware that we're neither alone nor the smartest thing in the universe."

Having found the signal, the institute envisions that enthusiasm on Earth will spur humans to build larger dishes more capable of receiving weak signals.

It is unlikely that Earth and an advanced civilization far from the sun will engage in much communication. That's because it can take years for a signal to travel from one planet to the other. The closest star, Alpha Centauri, is only 4.3 light-years away. If an advanced civilization exists on a (yet-unseen) planet around the star, it would take over eight years for a signal to travel from Earth to that world and back.

In addition to accidental broadcasts, Earth has sent a handful of messages into space. In 1974, a simple message was transmitted from Arecibo Observatory in Puerto Rico. Both NASA and Russia have since sent a handful of brief, deliberate signals into space since then, according to the SETI Institute.

Verify and confirm

When an interesting signal is detected, scientists must first verify it came from beyond Earth. By confirming observations with another radio telescope, they can make sure they have not picked up a human-created signal. Even if the original detector determines that the source didn’t come from Earth, additional instruments provide “duplication,” an important part of the scientific process.

"Once an artificial signal is confirmed as being of extraterrestrial intelligent origin, the discovery will be announced as quickly and as widely as possible," said the SETI Institute.

"There will be no secrecy, and indeed getting the word out quickly is important as there would be an urgent need to have astronomers world-wide monitor any detected signal 24 hour a day."

Other seekers

While the SETI Institute is easily the most well-known seeker of signs of advanced civilizations, they are not the only ones. The University of California, Berkeley has several SETI programs under way, including one using the Arecibo Observatory. Italy's University of Bologna also has a radio SETI search in progress. Both Berkeley and Harvard University in Boston have optical SETI searches in progress.

In a 2014 presentation to Congress, Shostak predicted that life would be found on worlds other than Earth in the near future.

"It's unproven whether there is any life beyond Earth," Shostak said. "I think that situation is going to change within everyone's lifetime in this room."

Even if no sign of an advanced civilization is found, the SETI Institute remains optimistic.

According to their website, "We are just scratching the surface of what a modern search can do. Failure to find a signal wouldn’t prove that we’re the only thinking beings in the Galaxy. After all, absence of evidence is not evidence of absence."

"The SETI Institute intends to press the search. Needless to say, the march of technology and new scientific discoveries will influence future SETI strategies. But giving up is not in the cards. Christopher Columbus did not turn around simply because he failed to find any new lands during his first few days at sea."

Follow Nola Taylor Redd on Twitter @NolaTReddor Google+. Follow us at@Spacedotcom, Facebookor Google+. Originally published on Space.com.

Editor's note: This article was corrected to reflect the accurate distance to Alpha Centauri.