Astronomy and space news summarized by Don Lynn from NASA and other sources
Perseverance Lands – NASA’s latest planetary mission, a rover named Perseverance, landed on Mars February 18. The rover weighs over a ton on Earth, and is seven feet high and ten feet long, plus an arm that extends out. There are 23 cameras onboard, including ones with color, zoom and stereo capabilities. Its onboard instruments include spectrometers, a ground-penetrating radar, microphones, a weather station and an experimental device to produce oxygen from the atmospheric carbon dioxide. The rover used a heat shield, a supersonic parachute and a rocket-powered sky crane to land, similar to NASA’s previous rover Curiosity. Improving on the previous rover, it included an avoidance system with a map of all the dangerous rocks, cliffs, soft sand and other places in the area to avoid. Another upgrade was a triggering system to open the parachute at the optimal time, taking into consideration the atmospheric conditions it encountered, rather than based on the planet’s average conditions used on previous landings. The entire landing sequence is controlled by computers on the spacecraft, due to the 11 minutes it takes to send, at the speed of light, any commands from Earth. The Mars Reconnaissance Orbiter (MRO), a mapping satellite in orbit around Mars, relayed data during the landing to the NASA radio dish in Spain. MRO managed to take a snapshot of the rover descending under its parachute.
In addition to its scientific instruments, a small helicopter named Ingenuity is fastened under the rover. It will be released onto the ground in a month or so, once a suitable location for its takeoffs is found. It will then perform five flights to test how a helicopter can aid in finding places for a rover to visit or travel through. Flying on Mars is not easy, as the atmosphere is more than 100 times thinner than Earth’s. This will be the first powered aircraft on another planet, though two unpowered balloons were used on Venus decades ago. After the helicopter test flights, it will not try to keep up with Perseverance as the rover drives off to continue its mission. That mission is to explore Jezero Crater, searching for signs of ancient life and collecting soil samples to be returned to Earth by future probes. Jezero was a lake three or four billion years ago, and the deltas where two rivers entered the lake remain little changed since the lake, along with the rest of the planet, dried up. Scientists believe such deltas are likely places to have preserved evidence of ancient life, if such developed on Mars. The rover’s landing hazard avoidance system produced the landing spot only 1.2 miles from the larger river delta in Jezero, which is only a few days drive for Perseverance.
More Mars Missions – Every 26 months the Earth and Mars line up to allow optimal travel between the two planets. That happened about last July, and the three missions to Mars launched then arrived at the Red Planet in February. On the 9th, the Hope spacecraft from the United Arab Emirates entered into Martian orbit. Using infrared and ultraviolet spectrometers, it will study the various regions of the atmosphere. It is designed to complement previous Martian atmospheric missions, such as MAVEN. It is the first planetary mission by any Arab nation, and was a joint effort with U.S. universities and was launched from Japan.
China’s Tianwen 1 mission entered Mars orbit February 10. The craft’s orbiter will remain in orbit to study the Red Planet from 165 miles up, while its lander is scheduled to leave orbit about May and deploy a rover onto the planet’s surface. The rover has a radar that can penetrate ground to a depth of about 100 yards.
Currently operating spacecraft at Mars consist of eight orbiters, two rovers, and a lander. With the successful landing of the Chinese spacecraft, there will be three rovers and two landers. The orbiters represent six different space agencies. Up until now, all successful landers and rovers operated on Mars have been NASA products, but should change with the success of the Chinese mission.
Martian Atmosphere – Astronomers have been trying to determine when and how Mars lost its atmosphere, chiefly by extrapolating back from current measurements of atmospheric loss. The evidence of water flowing on the planet’s surface billions of years ago indicates that it once had a thicker atmosphere. A new study by researchers at the University of California, Berkeley of the current atmospheric loss showed that escaping gases should strike the Martian moon Phobos and accumulate as a historic record. The Japan space agency is planning a mission to Phobos in 2024 with sample return. Scientists are hoping that with that data, they can put together a history of Martian atmospheric loss.
Venus Plate Tectonics Lacking – A new study by astronomers at Brown University looked at Mead, the largest impact basin on Venus, and compared it with computer simulations of similar such impacts. They found that to form the crater seen today, the heat flow and thickness of the crust at the time of impact did not match that of a planet with moving surface plates. This means that if Venus ever had plate tectonics, it ended before the Mead impact, estimated to have occurred between 0.3 and 1 billion years ago.
Mercury Impact – A new study of old MESSENGER data by physicists at NASA’s Jet Propulsion Laboratory, showed that the spacecraft observed a meteoroid striking the surface of the planet Mercury. The impact itself was not seen, but the material thrown up over 3,000 miles into space by the impact was imaged. The BepiColombo spacecraft on its way to Mercury will look for similar events.
Titan Sea – New analysis of Cassini spacecraft data by researchers at Cornell shows that Kraken Mare, the largest liquid methane-ethane sea on Saturn’s moon Titan, reaches a depth of at least 1,000 feet. The depth of smaller Titan seas had been previously determined. The composition of Kraken Mare was also determined, and it was found to be mostly methane, with some ethane. This was a surprise because previous estimates based on the body’s latitude had shown it was likely mostly ethane. Kraken Mare is nearly as large as all of the earthly Great Lakes combined.
Earth Trojan – A Trojan-type asteroid is one that shares a planet’s orbit, but remains ahead or behind the planet, near one of its gravitationally-stable Lagrange points. The original ones were found in Jupiter’s orbit, where about 9,000 are now known, but a few have been found in the orbits of most other Solar System planets. Earth had only one known, until now. A second has been found by the Pan-STARRS 1 survey at Haleakala Observatory, Hawaii. Dubbed 2020 XL5, it travels in a wide loop around Earth’s L4 Lagrange point, so wide it occasionally approaches Venus. From its brightness, the astronomers estimate it is a few hundred yards across. An analysis of the orbit shows it will be stable for 2,000 to 4,000 more years, but then will be perturbed away from the L4 region by gravitational interactions with other Solar System bodies. Because Earth Trojans are small and close to the Sun from our viewpoint, they are hard to find. Astronomers believe that there may be many undiscovered ones, so the search for more of them continues.
Resonant Planets – Observations by astronomers at the University of Geneva using Cheops, a European space telescope dedicated to precision follow-up observations of exoplanets orbiting nearby stars, revealed that five of the six exoplanets orbiting a star 200 light-years away in the constellation Sculptor are in resonance with each other. This resonance is given as 18:9:6:4:3, meaning that the innermost planet of these five makes 18 orbits in the same time period as the next planet outward makes nine orbits, and so on. The exoplanet closest to the star does not participate in the resonance seen with these five outer planets. Scientists then looked for any pattern in the sizes, masses and densities of the observed planets, but could find none. It has been hypothesized that the way in which planets form should yield a progression in sizes, masses or densities. All six of the planets are closer to their star than the habitable zone, meaning that they are all too hot for liquid water to exist on their surfaces. Astronomers plan to look for more planets in this system, possibly in the habitable zone.
Clear Skies – Astronomers at the Harvard and Smithsonian Center for Astrophysics have determined that a gas giant exoplanet discovered in 2012 has an atmosphere free of clouds or haze. Spectroscopic observations using the Hubble Space Telescope showed that the spectrum of sodium penetrated the atmosphere, which does not happen if there are clouds or haze. The planet is known as WASP-62b and is about 575 light-years away. It is about half the mass of Jupiter and orbits close enough to its star to be classified as a “hot Jupiter” planet. Only one other exoplanet with a clear atmosphere is known. Scientists hope they may able to determine the surface composition of a planet with a clear atmosphere.
Sky Brightness Measured – Astronomers would like to measure the brightness of the night sky in between stars and galaxies that can be resolved. Unfortunately the dust within the Solar System outshines whatever is there between the stars. Fortunately, the New Horizons spacecraft, after its encounter with Pluto and a Kuiper Belt object, has traveled beyond the Solar System dust. Using its on-board camera, astronomers at the Space Telescope Science Institute measured the brightness of the sky between objects. The result was a brightness half of one previous estimate and twice another. It is expected that galaxies too small or too distant to resolve make up the light measured.
Gravitational Lenses Found – Astronomers love to find gravitational lenses. These are where the massive gravity of a galaxy or a cluster of galaxies bends light, and there happens to be one or more galaxies almost perfectly lined up behind. A number of things can be calculated from the shape of gravitationally lensed images, including the location of dark matter in the foreground object and the expansion rate of the Universe. But because astronomical objects rarely line up well, such lensed images are rare, occurring at only about 1 in every 10,000 massive galaxies, making it tedious to find new gravitationally lensed images. In response, astronomers at the University of San Francisco and Lawrence Berkeley National Laboratory taught a computer to search for them. They fed it a pile of images marked lensed or not-lensed, and instructed it to determine how to recognize similar objects. Then they fed it the images from surveys of a large fraction of the sky, known as the DESI Legacy Imaging Surveys. The computer found 1,210 previously unknown gravitational lenses, about doubling the number known.
Intermediate-Mass Black Holes – Scientists know of many black holes at the centers of galaxies which have masses millions of times that of the Sun. They also know of numerous black holes with the mass of a single collapsed star. But there are only a handful of known black holes with intermediate masses between these, and many of these are only considered candidates in need of further confirmation, and the hunt for these missing black holes is ongoing. One possible place they might form is at the center of tightly bunched star clusters, where more massive objects sink to their centers over time, while less massive ones move to the outskirts. This is caused by the way objects gravitationally throw each other around during close chance encounters. Astronomers theorized that solar-mass black holes in tight globular star clusters ought to sink to the center, where they could merge to form intermediate mass black holes. A new study by astronomers at the Paris Institute of Astrophysics, tracked the movements of stars in the globular cluster NGC 6397 to calculate the locations of masses that affected its stars’ orbits. They hopeed to find a huge mass at the center of the cluster that could be an intermediate-mass black hole. Instead, they found a number of unseen masses spread about the central region. They think that the expected solar-mass black holes likely exist, and apparently sank to the center, but failed to merge into a single intermediate-mass black hole. The intermediate black hole mystery continues.
Radar Astronomy Experiment – An experiment by the National Radio Astronomy Observatory, Green Bank Observatory and Raytheon to image Solar System objects with radar was successful, using one radiotelescope to broadcast radio waves and several others linked together to receive the echoes. The Green Bank telescope broadcast, and the Very Long Baseline Array listened for the return signals. The use of an array as a receiver gives far better resolution in the radar images than is possible with a single receiver. When a more powerful transmitter is built than the one used for the experiment, this technique could image objects as far as Neptune. This could replace or exceed much of the radar capability lost with the collapse of the Arecibo radiotelescope. The team’s experiment was planned before that collapse. Coincidentally, the Green Bank Telescope collapsed in 1998, but was rebuilt with more capability in about five years. The experiment imaged the area where Apollo 15 landed on the Moon.
No Supernova Yet – A new study led by researchers at the Australian National University, took a close look at the star Betelgeuse, in response to theories that its recent dimming might portend its explosion, found that the red supergiant is in the early part of its helium-fueled phase, meaning it won’t be ready to go supernova for more than 100,000 years. It’s observed brightness cycles of about 185 and 400 days match what is expected for a star in this phase. The study found also that its mass, radius, and distance are all somewhat smaller than previously accepted values. The new measurements put it at about 16.5 to 19 solar masses, 750 times the Sun’s radius and 530 light-years away. The unexpected dimming observed a few months ago was caused, as some previous studies suggested, by a dust cloud.
Wrong-Way Planets – Astronomers at Aarhus University found a pair of exoplanets orbiting their star, dubbed K2-290, in the opposite direction to that star’s rotation. Only a few such cases are known. Planets normally form in a disk that shares the rotation direction of its star, as the star and disk formed at the same time and nearly the same place. To get these wrong-way planets, something has to be changing the planets’ orbits or the stars’ rotation after formation. For these newly discovered planets, a companion star orbiting the main star is gravitationally disturbing the planets’ orbits. The star doesn’t so much reverse the planet’s orbit, but slowly tilts the plane of the orbit until that plane has tipped over. However, this cannot explain many of the other wrong-way planets discovered, so more observations are needed.
Solar Activity – Astronomers have records of the Sun’s activity from counting sunspots and the like, only since the telescope was invented in the early 1600s, and even then, details from the earlier years are somewhat sparse. A team of scientists at ETH Zurich using new mass spectrometers more sensitive than ever before, have measured the carbon-14 isotope content embedded in tree rings of known ages and calculated solar activity back about 1,000 years. The amount of carbon-14 in the atmosphere, which gets taken up by trees as they grow, depends on the strength of cosmic rays striking the Earth, and cosmic ray strength depends on the Sun’s magnetic field, which varies with solar activity. The team confirmed a known solar outburst in the year 993 and discovered new ones in 1052 and 1279. They hope also to extend this technique even further back using older wood samples of known age, which do exist.