A massive, quiescent galaxy at a redshift of 3.717
Nature 544, 7648 (2017). doi:10.1038/nature21680
Authors: Karl Glazebrook, Corentin Schreiber, Ivo Labbé, Themiya Nanayakkara, Glenn G. Kacprzak, Pascal A. Oesch, Casey Papovich, Lee R Spitler, Caroline M. S. Straatman, Kim-Vy H. Tran & Tiantian Yuan
Finding massive galaxies that stopped forming stars in the early Universe presents an observational challenge because their rest-frame ultraviolet emission is negligible and they can only be reliably identified by extremely deep near-infrared surveys. These surveys have revealed the presence of massive, quiescent early-type galaxies appearing as early as redshift z ≈ 2, an epoch three billion years after the Big Bang. Their age and formation processes have now been explained by an improved generation of galaxy-formation models, in which they form rapidly at z ≈ 3–4, consistent with the typical masses and ages derived from their observations. Deeper surveys have reported evidence for populations of massive, quiescent galaxies at even higher redshifts and earlier times, using coarsely sampled photometry. However, these early, massive, quiescent galaxies are not predicted by the latest generation of theoretical models. Here we report the spectroscopic confirmation of one such galaxy at redshift z = 3.717, with a stellar mass of 1.7 × 1011 solar masses. We derive its age to be nearly half the age of the Universe at this redshift and the absorption line spectrum shows no current star formation. These observations demonstrate that the galaxy must have formed the majority of its stars quickly, within the first billion years of cosmic history in a short, extreme starburst. This ancestral starburst appears similar to those being found by submillimetre-wavelength surveys. The early formation of such massive systems implies that our picture of early galaxy assembly requires substantial revision.
Technology Infused: The Lunar polar Hydrogen Mapper (LunaH-Map) mission is a CubeSat that will detect the amount of hydrogen at the moon’s South Pole.LunaH-Map Spacecraft Design (cutaway views).
Designed to fly around the moon in a polar orbit at low altitude (5-12 km), LunaH-Map will carry two newly designed neutron spectrometers to produce highresolution maps of near-surface hydrogen. Previous moon missions have indicated that there is an abundance of hydrogen near the lunar poles, but the exact locations were not determined.
The presence of hydrogen indicates the presence of water, and LunaHMap will provide important constraints on the location and abundance of ice deposits near the lunar South Pole. The spectrometers on LunaH-Map will measure the energies of neutrons that have interacted with and subsequently leaked back out of the material in the top meter of the lunar surface. To accomplish this task, the mission will employ new technology—an elpasolite scintillation detector—in an array of neutron detectors mounted to one face of the spacecraft. These new detectors enable efficient neutron detection capability in a small package, making them ideal for use on a CubeSat platform.
Impact: LunaH-Map will produce maps of hydrogen abundance with the highest spatial resolution ever acquired by a neutron detector from orbit, and will demonstrate the capability of a CubeSat platform to acquire neutron counts from planetary surfaces. Understanding the distribution of hydrogen on the surface of the moon will help NASA plan future missions to the moon, especially missions that will land on the surface. Knowing the location and volume of ice deposits will also be vital to future moon missions that plan to make use of in situ resources—for example, a human mission to the moon. LunaH-Map will also use a highly efficient ion propulsion system to maneuver itself from the Space Launch System (SLS) into a stable lunar orbit, and finally a science mapping orbit. LunaH-Map and Lunar IceCube will be the first two interplanetary CubeSats to demonstrate this technology in space on a small spacecraft platform.Orbit ground track shown in red for the entire 60 (Earth) day LunaH-Map science phase:141 passes over target area initially (and periodically) centered on Shackleton Crater withclose-approach of 5 km at each perilune crossing. Yellow circle denotes LunaH-Mapaltitude of 8 km; green circle denotes LunaH-Map altitude of 12 km.
Status and Future Plans: LunaH-Map is one of 13 CubeSats scheduled for launch on the first integrated flight of NASA’s Space Launch System and Orion spacecraft in 2018. LunaH-Map is being designed, built, and tested at Arizona State University. Industry partners will design, build, and deliver the spectrometers for integration into the spacecraft.Busek’s 65W iodine-fueled ion propulsion system “BIT-3,” currently scheduled to fly onthe LunaH-Map and Lunar IceCube missions.
Sponsoring Organization: PSD provides funding for the LunaH-Map effort via the PICASSO program. PI, Craig Hardgrove, resides at Arizona State University. STMD’s SBIR program provides funding for technology development related to the detector component of the spectrometer to Radiation Monitoring Devices, Inc. and the ion propulsion system to Busek Co. Inc.Master Image:
Planetary science: Reckless orbiting in the Solar System
Nature 543, 7647 (2017). doi:10.1038/543635a
Authors: Helena Morais & Fathi Namouni
Planets and most asteroids revolve around the Sun in the same direction. But an asteroid that shares Jupiter's orbit has been revolving in the opposite direction for about a million years. See Letter p.687
A retrograde co-orbital asteroid of Jupiter
Nature 543, 7647 (2017). doi:10.1038/nature22029
Authors: Paul Wiegert, Martin Connors & Christian Veillet
Recent theoretical work in celestial mechanics has revealed that an asteroid may orbit stably in the same region as a planet, despite revolving around the Sun in the sense opposite to that of the planet itself. Asteroid 2015 BZ509 was discovered in 2015, but with too much uncertainty in its measured orbit to establish whether it was such a retrograde co-orbital body. Here we report observations and analysis that demonstrates that asteroid 2015 BZ509 is indeed a retrograde co-orbital asteroid of the planet Jupiter. We find that 2015 BZ509 has long-term stability, having been in its current, resonant state for around a million years. This is long enough to preclude precise calculation of the time or mechanism of its injection to its present state, but it may be a Halley-family comet that entered the resonance through an interaction with Saturn. Retrograde co-orbital asteroids of Jupiter and other planets may be more common than previously expected.
Astronomy: Landslides cause comet eruptions
Nature 543, 7647 (2017). doi:10.1038/543593c
The collapse of cliffs on comets can create plumes of gas and dust, which contribute to comets' characteristic tails.Such outbursts are frequent, but their cause has been unclear. Maurizio Pajola at the NASA Ames Research Center in Moffett Field, California, and his colleagues analysed
Planetary science: Titan's electrified dunes
Nature 543, 7647 (2017). doi:10.1038/543592b
The dunes of Saturn's largest moon, Titan, may be held together by static electricity.Grains of sand acquire electrostatic charge as they rub against each other, but on Earth this effect is generally negligible because gravity and a high density of heavy silicate particles minimize