Scientists may have figured out what the core of our planet is made of. We don’t have direct access to the core — the best we can do is boreholes and, sometimes, magma. For some years, scientists have been pretty sure that the inner core of the Earth is made of 85% iron and 10% nickel. What’s in the other 5% has remained elusive, but now scientists from Tohoku University in Japan have put forth a study that may have identified that 5% as silicon. They basically built a stripped-down scale model of the planet’s interior, subjecting different combinations of elements to extreme temperatures and pressures and then testing them with seismometers to determine which reacted in a way that agreed with what we see our planet do. This report is interesting in light of other recent work on the hypothesized origin of the moon, which argued that a silicon-rich exoplanet could have crashed into ours and been subsumed, whereafter the moon formed out of that combined, mostly molten bulk.
NASA scientists used the Mars Reconnaissance Orbiter to make a cool composite shot of the Earth and the Moon, as they appear from Mars. The image is blurry, because it was taken from freakin’ Mars, so the MRO had to zoom in the whole way. This is the same adept spacecraft that mission scientists pressed into service to find the crash site of the ExoMars rover after it lost its cool on the descent from orbit to the Martian surface. Check out what it sees:
Earth and the moon, as seen from Mars by the MRO.
NASA is sending out two new Discovery missions to the outer solar system. One of them is called Lucy, and it’s supposed to launch in 2021 headed to one of the asteroids that hang out at Jupiter’s leading and trailing Lagrange points. They’re called Trojan asteroids, and while five other planets have such asteroids, Jupiter has the most, by orders of magnitude. Scientists believe the Jupiter Trojans are “relics” of the early solar system — these chunks of debris orbiting with Jupiter are of the same mass of debris that aggregated to form the rest of our planets.
Lucy’s sister Discovery mission, Psyche, is headed in 2023 for a fossil from deep time: 16 Psyche, a huge metallic asteroid that we think used to be the core of an aggregating planet that got completely bashed to smithereens, way back in our solar system’s infancy. Both spacecraft will be toting sweet multispectral cameras, spectroscopy instruments and radio Doppler equipment, and given that 16 Psyche is supposed to be metallic, Psyche may also have a magnetometer aboard. NASA will be working with Lockheed Martin to build Lucy, and for Psyche, with the JPL, Space Systems/Loral and Arizona State University. Lucy will also involve the Southwest Research Institute, and Psyche the Goddard Space Center.
Nobody has found Planet 9 yet, but at least we’ve almost figured out where to look. Image: NASA
Putative Planet 9 has another possible origin story. If it coalesced around our sun, it’s almost certainly an ice giant like Neptune. And a slow giant indeed: it would make Pluto’s 248-year orbit look positively sprightly, with a possible orbital period of some 20,000 years. But scientists working with models ran the clock back and discovered that Planet 9 could also be a rogue planet that formed around another star and then was, for whatever reason, flung off into space, after which Sol (theoretically) captured it.
Hubble is taking a little while to scout out the Voyagers’ paths through interstellar space. While the Voyagers head ever outward at two different angles away from the ecliptic, Hubble looked straight down the line-of-sight paths of the sibling spacecraft, to determine what lies ahead for their long haul. Mostly it’s vacuum, with a side of clouds of cold gas. But it’s not all about the Voyagers. Their direct measurements of the interstellar medium, along with Hubble’s observations on what lies where, will be important for planning true interstellar missions such as the future Breakthrough Starshot, according to Julia Zachary, who presented findings from the Hubble-Voyager collaboration at a meeting of the American Astronomical Society.
Speaking of the planning stages of Breakthrough Starshot, they’re going to upgrade the ESO’s Very Large Telescope so they can use the radio interferometer to stare at Alpha Centauri — presumably to make sure there’s something there worth sending a fleet of tiny laser-propelled nano-spacecraft pelting after at a tidy 0.2 C. The upgrade will trick out the VLT’s VISIR instrument, adding a coronagraph, adaptive optics and possibly better calibration equipment, in exchange for telescope time.