Selected Summaries of Space News
by Don Lynn
Asteroid Sampled
Hayabusa2 (a Japanese spacecraft) has touched down on its target, the asteroid Ryugu, and completed a procedure to fire a projectile into it and collect the debris blown off. Another sample will be taken from inside a fresh impact crater to find out what the inside of the asteroid is made of. (Material on the surface has been subjected to millions of years of space weathering caused by radiation and micrometeorite impacts, so it won’t chemically be the same as the interior.) How will the spacecraft controllers find a fresh impact? They will make it by firing a huge impactor that is expected to make a crater two yards across.
Martian Air Pressure
InSight landed on Mars in November and has been sending weather reports back to Earth. Among its instruments is the most precise atmospheric pressure sensor ever sent to Mars. As expected, the pressure changes daily with air temperature, rising with lower temperature. Unexpectedly, the pressure has extra peaks at about 7 AM and 7 PM local Martian time.
You may ask why there is a pressure sensor on a mission to measure quakes. The ground actually moves ever so slightly with changes in air pressure, and those movements have to be subtracted from what the seismometer measures, in order to record only the quakes.
More About InSight
InSight is in the process of hammering its heat-flow probe into the Martian soil. In order to get away from any temperature changes near the surface, it needs to be pounded 10-16 feet deep. It will measure the heat flowing from the core of the planet, and how well the soil conducts heat. As of this writing, the hammer has hit a rock about half a meter (20 inches) below the surface. Controllers are taking a couple of weeks to determine the next moves. The probe has already pounded past one rock. The probe’s location was chosen because it was rock-free, at least as far as could be seen from above.
Tails of the Hyades
Open star clusters form most of their stars during the initial collapse of a gas cloud into stars. Then over hundreds of millions of years, gravitational disturbances force stars to wander off, and eventually the cluster is too spread out to distinguish. A new study was made of the Hyades open cluster, using data from Gaia, which very precisely measured positions and motions of more than a billion stars.
The study found about 500 stars that were moving away from the Hyades, and so were part of that cluster in the past. They are concentrated in two tails of stars, one in front and one behind (relative to the cluster motion). The tails extend up to 650 light-years from the cluster. This is the dissipation of an open cluster caught in action, and the first time such tails have been found about an open cluster, though they are often seen about galaxies or globular clusters.
Unusual Nova
Astronomers studying a nova in the Andromeda Galaxy have found a huge shell of material surrounding the nova. This particular star has been going nova about every year, more frequently than any other known. The shell must have been ejected by the previous nova eruptions—its size (almost 400 light-years across) suggests that it must have been erupting regularly for millions of years.
One type of nova occurs when a very close companion star dumps gas onto a white dwarf star until the gas undergoes a nuclear explosion. Theory has it that repeated accumulations of gas will eventually push the white dwarf’s mass past the critical mass that causes a supernova, which will obliterate the star.
Milky Way Mass
New data from the Gaia and Hubble space telescopes has given extremely precise positions and motions in three dimensions for the globular clusters orbiting our Milky Way galaxy. From this, scientists have calculated the total mass (both ordinary and dark matter) of the galaxy: 1.5 trillion solar masses. [Most of this mass is thought to be dark matter. —Ed.]
That mass had been difficult to determine, because it requires measuring the orbits of objects outside the galaxy but close to it, and the extent of the halo of stars and the halo of dark matter are not well known. Consequently, past galaxy mass measurements have varied greatly. The scientists believe that they have accounted for all mass out to a million light-years from the center of the Milky Way.
Geocorona Measured
The Earth is surrounded by an extremely thin cloud of hydrogen, known as the geocorona. It is a result of water vapor in the upper atmosphere being broken down into its hydrogen and oxygen, and the light hydrogen then escaping into space.
Scientists who wanted to know the size of the geocorona studied archived ultraviolet observations from the SOHO solar space telescope—occasionally, the Earth and its geocorona pass through the telescope’s field of view. The geocorona was found to extend as much as 390,000 miles from Earth—the Moon’s orbit actually lies within it.
Results from the new study show that sunlight pushes the geocorona closer to Earth on the daylight side, and that the cloud is extremely thin (about three atoms per cubic inch at the Moon’s distance). However, that is enough to somewhat interfere with any ultraviolet observations that astronomers might want to make from future installations on the Moon.
Interestingly, the geocorona was discovered in ultraviolet observations made by equipment placed on the Moon by Apollo 16 astronauts. Little did they realize that the observations were being made inside the geocorona.
Huge Stellar Flare
Astronomers using the James Clerk Maxwell Telescope in Hawaii have discovered flares from a still-forming young star that are 10 billion times more powerful than flares from our Sun. Apparently, material is still falling into this star in bursts, causing such flares. Astronomers believe that the star is spinning faster than the disk of material feeding it, resulting in twisting of the star’s magnetic field until it snaps and reconnects, forcing big chunks of material to fall into the star.
The Maxwell Telescope operates in sub-millimeter wavelengths, that portion of the light spectrum between long infrared and short radio waves. This is the first time such flares have been seen in sub-millimeter wavelengths, though similar events have been observed in X-rays, radio, and infrared. The star is in the Orion Nebula, about 1500 light-years away.
Oldest White Dwarf Found
A volunteer citizen-scientist has discovered the oldest known white-dwarf star, and it has been found to have a ring of dust (possibly a double ring) about it. After white dwarf stars form, their nuclear reactions stop, and they then just slowly cool off. Since this is the coolest known white dwarf, it must be the oldest. Whatever is feeding material into the ring around it must therefore have been acting for billions of years.
Theory has it that such rings surrounding white dwarfs dissipate in less than 100 million years unless something is replenishing the ring material. The best theory is that collisions in an asteroid belt encircling the star are producing the material. The citizen-science project was looking through WISE infrared data to find brown dwarfs (and Planet 9), but it also stumbled on this cool white dwarf. The project, called “Backyard Worlds: Planet 9,” in its first two years has found more than 1,000 brown dwarf candidates, but not Planet 9.
Super-Puffs
There are half a dozen known super-puffs, exoplanets about the size of Neptune but with a lot less mass, and therefore lower density. They must also consist mostly of gas and be fairly warm to have density this low. The problem is, the temperature required by the density should have already boiled off the atmosphere. A new paper suggests a solution: if outflows in the atmosphere constantly circulate dust, that dust could prevent the atmosphere from boiling away. These super-puffs share another mystery: they have no spectral lines. Dust would explain that, too.
LOFAR
The first data release has been made from LOFAR (low frequency radio telescope array). Though it covers only 2% of the sky scheduled for survey, it has discovered 300,000 new radio sources, many of them radio galaxies and quasars. Comparison with optical sky surveys shows that about 70% of the radio sources are objects already known in visible light.
An interesting finding is that all of the fairly massive galaxies have jets near their cores, which can be seen in low-frequency radio. Also found was that not only interacting galaxies, but isolated ones, are emitting radio, though less powerfully. LOFAR consists of 50 locations, each typically with an array of 2,000 antennas, connected to a supercomputer by fiber optics. They are spread out all over Europe, with the biggest concentration in the Netherlands.
Moon Lander Launched
More than a decade ago, Google and the X Prize Foundation announced a competition to win $30 million for the first privately sponsored space mission to land on the Moon and perform certain tasks, including sending pictures back. The deadline was eventually extended to March 2018. Though dozens of groups entered, no one finished on time.
This February 21st, a team from the competition launched their Moon lander named Beresheet, built by SpaceIL (a nonprofit organization in Israel), even though there is no longer a prize. It launched aboard a SpaceX rocket that also carried two communications satellites. This is the first Moon lander launched from the USA since Apollo 17, in 1972. Landing is scheduled for about April 11, and the craft is designed to operate for a few days on the surface.
Crew Dragon Test Flight
SpaceX made an unmanned test flight of their spacecraft, the Crew Dragon, reaching and docking with the International Space Station. A few days later, it returned to Earth, soft-landing in the Atlantic under four huge parachutes. The Crew Dragon needs to pass one more test, that of its emergency escape rocket system, before it will be ready for a flight with people aboard. That flight could happen as soon as July.
Boeing, like SpaceX, is under contract from NASA to produce a craft to take people into space, and hopes to also make a crewed flight this year. American astronauts have not launched in American spacecraft since July 2011, when the Space Shuttle made its last flight. The United States has been buying rides into space on Russian rockets.