Scientist captures new images of Martian moon Phobos to help determine its origins

Christopher Edwards, assistant professor in NAU's Department of Astronomy and Planetary Science, just processed new images of the Martian moon Phobos that give scientists insight into the physical properties of the moon and its composition. The images of the small moon, which is about 25 kilometers (15 miles) in diameter, were captured by NASA's 2001 Mars Odyssey orbiter. When reviewed in combination with three previously released images, these new images could ultimately help settle the debate over whether the planetary body is a "captured asteroid"--pulled into perpetual orbit around Mars--or an ancient chunk of Mars blasted off the surface by a meteorite impact. Along with scientists at NASA's Jet Propulsion Lab and Arizona State University, Edwards used the Thermal Emission Imaging System (THEMIS) onboard the 2001 Mars Odyssey orbiter to capture the images from about 6,000 kilometers (3,700 miles) above the moon's surface to measure temperature variations during different phases--waxing, waning and full: 

+ An image taken on December 9, 2019, shows the surface of Phobos at its maximum temperature, 81 degrees Fahrenheit (27 degrees Celsius).

+ An image taken on February 25, 2020, shows Phobos while in eclipse, where Mars' shadow completely blocked sunlight from reaching the moon's surface. This event resulted in some of the coldest temperatures measured on Phobos to date, with the coldest being about -189 degrees Fahrenheit (-123 degrees Celsius).

+ On March 27, 2020, Phobos was observed exiting an eclipse, when its surface was still warming up.

Edwards has been a part of the THEMIS team since 2003. All of the THEMIS infrared images are colorized and overlain on THEMIS visible images taken at the same time, except for the eclipse image, which is overlain on a synthetic visible image of what Phobos would have looked like if it hadn't been in complete shadow.

"The THEMIS instrument is designed to look at the composition and physical properties of the surface of Mars under various conditions using its multi-wavelength visible and infrared cameras," Edwards said.

From the new images, he said, "We're seeing that the surface of Phobos is relatively uniform and made up of very fine-grained materials. These observations are also helping to characterize the composition of Phobos, which appears to be mostly basaltic. Future observations will provide a more complete picture of the temperature extremes on the moon's surface."

Odyssey is the longest-operating spacecraft around Mars, and has been orbiting the Red Planet for more than 18 years.

"In an effort to continue advancing new science from the Odyssey mission as it matures," Edwards said, "a couple of years ago we proposed we could look at Phobos as part of our extended mission proposal. That requires a BIG spacecraft maneuver, rotating it 180 degrees into a geometry in which it was never intended to operate."

"As far as Phobos goes," he said, "its origins are enigmatic. The orbit it is in is not very stable, and some scientists have proposed that the moon has been destroyed and reformed multiple times because of its orbital position. It also turns out that the orbit's exact geometry makes it hard to capture--so some teams have proposed it is derived from Mars. How that happened is not clear, either!

"Perhaps it's from a big meteorite impact that ejected material into the orbit, and the material grouped together to form Phobos. So that's why we're looking for the physical properties of the surface, which might help identify locations where we could see the primary composition and not just the fine-grained dust."

Edwards added, "JAXA, Japan's space agency, is sending a whole mission to investigate Phobos and Diemos (Mars' other moon) called the Martian Moons eXploration (MMX), so we're providing some good reconnaissance data for that upcoming mission!"

More details of China's space station unveiled

After the successful maiden flight of the Long March-5B large rocket and the testing of China's new-generation manned spaceship, more details of China's space station have been unveiled. The space station, expected to be completed around 2022, will operate in the low-Earth orbit at an altitude from 340 km to 450 km for more than 10 years, supporting large-scale scientific, technological and application experiments, according to a report in the People's Daily. The space station Tiangong, meaning Heavenly Palace, will be able to accommodate three astronauts in normal circumstances and up to six during a crew replacement. The station will be a T shape with the core module at the center and a lab capsule on each side. Each of the modules will be over 20 tonnes, with the total mass of the station about 66 tonnes, said Zhou Jianping, chief designer of China's manned space program. If China's Tiangong-1 and Tiangong-2 space labs are like one-bedroom apartments, the space station is equivalent to an apartment with three bedrooms, a living room, a dining room and a storage room, said Zhu Guangchen, deputy chief designer of the space station from China Academy of Space Technology (CAST). The core module of the station, named Tianhe, has a total length of 16.6 meters, a maximum diameter of 4.2 meters and a takeoff mass of 22.5 tonnes, and is currently the largest spacecraft developed by China.

The Tianhe core module will be the management and control center and the main living space of the crew, and will support some scientific and technological experiments.

The living space in the core module is about 50 cubic meters. Combined with the two lab capsules, the whole living space could be up to 110 cubic meters, according to CAST.

The core module has two berth ports connecting to the two lab capsules, and three docking ports for the crew spacecraft, cargo and other craft. It also has an exit for astronauts to conduct extravehicular activities. (Xinhua)

Starliner to go to ISS without crew in November, crewed flight set for next year

Boeing's Starliner spacecraft will refly its uncrewed test mission to the International Space Station (ISS) in November of this year, while the first crewed flight is planned for April 2021, a space source said. "The second flight of the Starliner spacecraft to the ISS without crew is expected in mid-November 2020, while the first flight with crew - in April 2021", the source said. In April, Boeing announced that it was going to refly its uncrewed orbital flight test after problems during its first flight in December 2019. In December 2019, the Starliner spaceship set off on its first test flight to the International Space Station, but docking was canceled after Starkiner failed to execute an orbit-insertion burn on schedule. Earlier in the day, the SpaceX rocket with NASA astronauts Bob Behnken and Doug Hurley lifted off to the International Space Station (ISS) in a second attempt, after Wednesday's launch was postponed due to bad weather conditions. The Boeing Starliner is a $4.2 billion next-gen crew capsule with a capacity of up to 7 astronauts, a free-flight operating capability of up to 60 hours, and the ability to remain docked in orbit for up to 210 days. It is designed to be launched by Atlas V non-reusable rockets, which use Russian-made RD-180 engines developed by NPO Energomash.

In Planet Formation, It's Location, Location, Location

Astronomers using NASA's Hubble Space Telescope are finding that planets have a tough time forming in the rough-and-tumble central region of the massive, crowded star cluster Westerlund 2. Located 20,000 light-years away, Westerlund 2 is a unique laboratory to study stellar evolutionary processes because it's relatively nearby, quite young, and contains a large stellar population. A three-year Hubble study of stars in Westerlund 2 revealed that the precursors to planet-forming disks encircling stars near the cluster's center are mysteriously devoid of large, dense clouds of dust that in a few million years could become planets. However, the observations show that stars on the cluster's periphery do have the immense planet-forming dust clouds embedded in their disks. Researchers think our solar system followed this recipe when it formed 4.6 billion years ago. So why do some stars in Westerlund 2 have a difficult time forming planets while others do not? It seems that planet formation depends on location, location, location. The most massive and brightest stars in the cluster congregate in the core, which is verified by observations of other star-forming regions. The cluster's center contains at least 30 extremely massive stars, some weighing up to 80 times the mass of the Sun. Their blistering ultraviolet radiation and hurricane-like stellar winds of charged particles blowtorch disks around neighboring lower-mass stars, dispersing the giant dust clouds."Basically, if you have monster stars, their energy is going to alter the properties of the disks around nearby, less massive stars," explained Elena Sabbi, of the Space Telescope Science Institute in Baltimore and lead researcher of the Hubble study.

"You may still have a disk, but the stars change the composition of the dust in the disks, so it's harder to create stable structures that will eventually lead to planets. We think the dust either evaporates away in 1 million years, or it changes in composition and size so dramatically that planets don't have the building blocks to form."

The Hubble observations represent the first time that astronomers analyzed an extremely dense star cluster to study which environments are favorable to planet formation. Scientists, however, are still debating whether bulky stars are born in the center or whether they migrate there. Westerlund 2 already has massive stars in its core, even though it is a comparatively young, 2-million-year-old system.

Using Hubble's Wide Field Camera 3, the researchers found that of the nearly 5,000 stars in Westerlund 2 with masses between 0.1 to 5 times the Sun's mass, 1,500 of them show fluctuations in their light as the stars accrete material from their disks. Orbiting material clumped within the disk would temporarily block some of the starlight, causing brightness fluctuations.

However, Hubble detected the signature of such orbiting material only around stars outside the cluster's packed central region. The telescope witnessed large drops in brightness for as much as 10 to 20 days around 5% of the stars before they returned to normal brightness. They did not detect these dips in brightness in stars residing within four light-years of the center. These fluctuations could be caused by large clumps of dust passing in front of the star. The clumps would be in a disk tilted nearly edge-on to the view from Earth.

"We think they are planetesimals or structures in formation," Sabbi explained. "These could be the seeds that eventually lead to planets in more evolved systems. These are the systems we don't see close to very massive stars. We see them only in systems outside the center."

Thanks to Hubble, astronomers can now see how stars are accreting in environments that are like the early universe, where clusters were dominated by monster stars. So far, the best known nearby stellar environment that contains massive stars is the starbirth region in the Orion Nebula. However, Westerlund 2 is a richer target because of its larger stellar population.

"Hubble's observations of Westerlund 2 give us a much better sense of how stars of different masses change over time, and how powerful winds and radiation from very massive stars affect nearby lower-mass stars and their disks," Sabbi said.

"We see, for example, that lower-mass stars, like our Sun, that are near extremely massive stars in the cluster still have disks and still can accrete material as they grow. But the structure of their disks (and thus their planet-forming capability) seems to be very different from that of disks around stars forming in a calmer environment farther away from the cluster core. This information is important for building models of planet formation and stellar evolution."

This cluster will be an excellent laboratory for follow-up observations with NASA's upcoming James Webb Space Telescope, an infrared observatory. Hubble has helped astronomers identify the stars that have possible planetary structures. With Webb, researchers can study which disks around stars are not accreting material and which disks still have material that could build up into planets.

This information on 1,500 stars will allow astronomers to map a path on how star systems grow and evolve. Webb also can study the chemistry of the disks in different evolutionary phases and watch how they change, and help astronomers determine what influence environment plays in their evolution.

NASA's Nancy Grace Roman Space Telescope, another planned infrared observatory, will be able to perform Sabbi's study on a much larger area.? Westerlund 2 is just a small slice of an immense star-formation region. These vast regions contain clusters of stars with different ages and different densities.

Astronomers could use Roman Space Telescope observations to start to build up statistics on how a star's characteristics, like its mass or outflows, affect its own evolution or the nature of stars that form nearby. The observations could also provide more information on how planets form in tough environments.

MAVEN maps electric currents around Mars that are fundamental to atmospheric loss

Five years after NASA's MAVEN spacecraft entered into orbit around Mars, data from the mission has led to the creation of a map of electric current systems in the Martian atmosphere. "These currents play a fundamental role in the atmospheric loss that transformed Mars from a world that could have supported life into an inhospitable desert," said experimental physicist Robin Ramstad of the University of Colorado, Boulder. "We are now currently working on using the currents to determine the precise amount of energy that is drawn from the solar wind and powers atmospheric escape." Ramstad is lead author of a paper on this research published May 25 in Nature Astronomy. Earth has such current systems, too: we can even see them in the form of colorful displays of light in the night sky near the polar regions known as the aurora, or northern and southern lights. Earth's aurora are strongly linked to currents, generated by the interaction of the Earth's magnetic field with the solar wind, that flow along vertical magnetic field lines into the atmosphere, concentrating in the polar regions. Studying the flow of electricity thousands of miles above our heads, though, only tells part of the story about the situation on Mars. The difference lies in the planets' respective magnetic fields, because while Earth's magnetism comes from within, Mars' does not.

Planetary magnetic fields
Earth's magnetism comes from its core, where molten, electrically conducting iron flows beneath the crust. Its magnetic field is global, meaning it surrounds the entire planet. Since Mars is a rocky, terrestrial planet like Earth, one might assume that the same kind of magnetic paradigm functions there, too. However, Mars does not generate a magnetic field on its own, outside of relatively small patches of magnetized crust. Something different from what we observe on Earth must be happening on the Red Planet.

What's going on above Mars?
The solar wind, made up largely of electrically charged electrons and protons, blows constantly from the Sun at around a million miles per hour. It flows around and interacts with the objects in our solar system. The solar wind is also magnetized and this magnetic field cannot easily penetrate the upper atmosphere of non-magnetized planets like Mars.

Instead, currents that it induces in the planet's ionosphere cause a pile-up and strengthening of the magnetic field, creating a so-called induced magnetosphere. How the solar wind powers this induced magnetosphere at Mars has not been well understood until now.

As solar wind ions and electrons smash into this stronger induced magnetic field near Mars, they are forced to flow apart due to their opposite electric charge. Some ions flow in one direction, some electrons in the other direction, forming electric currents that drape around from the dayside to the nightside of the planet.

At the same time, solar x-rays and ultraviolet radiation constantly ionize some of the upper atmosphere on Mars, turning it into a combination of electrons and electrically charged ions that can conduct electricity.

"Mars' atmosphere behaves a bit like a metal sphere closing an electric circuit," Ramstad said. "The currents flow in the upper atmosphere, with the strongest current layers persisting at 120-200 kilometers (about 75-125 miles) above the planet's surface."

Both MAVEN and previous missions have seen localized hints of these current layers before, but they have never before been able to map the complete circuit, from its generation in the solar wind, to where the electrical energy is deposited in the upper atmosphere.

Directly detecting these currents in space is infamously difficult. Fortunately, the currents distort the magnetic fields in the solar wind, detectable by MAVEN's sensitive magnetometer. The team used MAVEN to map out the average magnetic field structure around Mars in three dimensions and calculated the currents directly from their distortions of the magnetic field structure.

"With a single elegant operation, the strength and paths of the currents pop out of this map of the magnetic field," Ramstad said.

The Red Planet's destiny
Without a global magnetic field surrounding Mars, the currents induced in the solar wind can form a direct electrical connection to the Martian upper atmosphere. The currents transform the energy of the solar wind into magnetic and electric fields that accelerate charged atmospheric particles into space, driving atmospheric escape to space.

The new results reveal several unexpected features particular to MAVEN's goal to understand atmospheric escape: the energy that drives escape appears to be drawn from a much larger volume than was often assumed.

Solar-wind-driven atmospheric loss has been active for billions of years and contributed to the transformation of Mars from a warm and wet planet that could have harbored life into a global cold desert. MAVEN is continuing to explore how this process works and how much of the planet's atmosphere has been lost.