Dark matter map from the Dark Energy Survey

Falcon Landing Attempts May Switch to Land

For the third time since January 10, Space Exploration Technologies (SpaceX) demonstrated the pinpoint accuracy of its guidance and navigational systems by bringing the spent first stage of its Falcon 9 rocket to a predetermined landing point. In the first and third cases, the destination was the Autonomous Spaceport Droneship, a football field-size barge converted to a seagoing landing platform. The second attempt was foiled by bad weather, but operators were nevertheless able to steer the rocket to within 10 meters of the ship before dunking it into the ocean.

Last Tuesday, after launching a Dragon cargo carrier to the International Space Station, controllers brought the Falcon 9 booster to a near-vertical touchdown on the drone ship, but due to what SpaceX CEO Elon Musk called “excess lateral velocity,” the rocket tipped over after landing and exploded. Later, Musk pointed a finger at a sticky valve that prevented the rocket’s systems from responding to sudden changes in orientation as quickly as needed. This resulted in overcompensation for a last-second tilt, causing an off-kilter landing. SpaceX president Gwynne Shotwell implied that the natural instability of an ocean platform contributed to the difficulty, expressing hope that the next first stage recovery would be attempted over land. No date for the next attempt was given, and the next Falcon 9 launch, currently scheduled for April 27, will use a rocket not equipped with the recoverable version’s landing gear.

However, SpaceX’s efforts appear to have spurred some out-of-the-box thinking on the part of rival United Launch Alliance (ULA), which on April 13 unveiled the successor to its venerable Delta and Atlas expendable launch vehicles. ULA’s versatile new rocket, still in development and dubbed Vulcan, features a reusable engine, developed in a partnership with Blue Origin, a private aerospace company created in 2000 by Amazon.com founder Jeff Bezos, which has also been quietly developing its own reusable spacecraft, called “New Shepard.” Interestingly enough, Bezos is also engaged in a legal dispute with SpaceX’s Musk over the patent rights to the concept of landing a reusable rocket stage on an ocean barge. Reusability had not been a feature of previous ULA rockets, but with SpaceX providing serious competition, ULA announced plans to recover Vulcan engines, with the goal of reducing launch costs. As opposed to SpaceX’s strategy of flying the entire first stage back to the ground, ULA’s plan involves jettisoning the rocket engines after their job is done, then parachuting them earthward and snagging them in mid-air with a waiting helicopter.

Vulcan’s first flight is currently scheduled for 2019. –Bing Quock

Brine on Mars

Two findings released this week point to the possibility of subsurface liquid salt water, or brine, on Mars.

On February 20, the HiRISE (High Resolution Imaging Science Experiment) camera on board NASA’s Mars Reconnaissance Orbiter imaged the mountainous peaks in Hale Crater, revealing long, dark, rusty streaks running down the slopes. These recurring slope lineae (RSL) may be the result of water seeping out from just below the surface, as the hot seasonal sun beats down on the martian southern latitude surface, bringing temperatures up to about 77 °F (25°C). If seeping water causes RSL in Hale crater, the water must be rich in salts to lower its freezing point significantly below the freezing point of pure H2O, notes Alfred McEwen, Principal Investigator of HiRISE.

The RSL seen in Hale crater are distinctive due to their unusually reddish color, potentially caused by oxidized iron compounds like rust, and that they start much earlier in the season, in early spring rather than midsummer.

Down on the Martian surface, NASA’s Curiosity rover is using its Rover Environmental Monitoring Station (REMS) to take a closer look at weather. A paper published this week in Nature uses data from the REMS to show that the right conditions for liquid brine may also exist in Gale Crater, closer to the equator. Curiosity identified calcium perchlorate in the soil of the crater, which can absorb water vapor from the atmosphere and reduce its freezing temperature. Scientists analyzed data from REMS, which monitors martian weather, including humidity and temperature, to determine if atmospheric water might mix with the surface.

“When night falls, some of the water vapor in the atmosphere condenses on the planet surface as frost, but calcium perchlorate is very absorbent and it forms a brine with the water, so the freezing point is lowered and the frost can turn into a liquid. The soil is porous, so what we are seeing is that the water seeps down through the soil. Over time, other salts may also dissolve in the soil and now that they are liquid, they can move and precipitate elsewhere under the surface,” explains Morten Bo Madsen, of the Niels Bohr Institute at the University of Copenhagen.

The findings come as a bit of a surprise. “Gale Crater is one of the least likely places on Mars to have conditions for brines to form, compared to sites at higher latitudes or with more shading. So if brines can exist there, that strengthens the case they could form and persist even longer at many other locations, perhaps enough to explain RSL activity,” said McEwen, who also co-authored Curiosity’s findings. –Elise Ricard

Mapping Dark Matter

How do you map something you can’t see? At this week’s meeting of the American Physical Society, researchers from the Dark Energy Survey (DES) released a map of dark matter in the cosmos. The map was created using data captured by the Dark Energy Camera, a 570-megapixel imaging device that is the primary instrument for DES.

A dark energy survey with dark matter results? Let’s shed a little light on this… Dark energy makes up over 63% of the Universe and is believed to be accelerating the expansion of the Universe. Dark matter makes up roughly a quarter of the mass-energy balance in the Universe and its effects can be seen by studying a phenomenon called gravitational lensing—the distortion that occurs when the gravitational pull of dark matter bends light around distant galaxies. Understanding the role of dark matter is part of the research program to quantify the role of dark energy, which is the ultimate goal of the survey.

The camera was constructed and tested at the U.S. Department of Energy’s Fermi National Accelerator Laboratory and is now mounted on the four-meter Victor M. Blanco telescope at the National Optical Astronomy Observatory’s Cerro Tololo Inter-American Observatory in Chile. The data were processed at the National Center for Supercomputing Applications at the University of Illinois.

“We measured the barely perceptible distortions in the shapes of about two million galaxies to construct these new maps,” team leader Vinu Vikram of Argonne National Laboratory says. Two million is only the beginning—these first maps cover only about three percent of the area of sky DES will document over its five-year mission. The survey has only completed its second year. As scientists expand their search, they will be able to better test current cosmological theories by comparing the amounts of dark and visible (what we like to think of as “normal”) matter.

Those theories suggest that, since there is much more dark matter in the Universe than visible matter, galaxies will form where large concentrations of dark matter (hence stronger gravitational influence) are present. So far, the DES analysis backs this up: the maps show large filaments of matter (in red, yellow, and brown, above) along which visible galaxies and galaxy clusters lie and cosmic voids (in blue) where very few galaxies reside.

“Our analysis so far is in line with what the current picture of the universe predicts,” says co-leader Chihway Chang of ETH Zurich. “Zooming into the maps, we have measured how dark matter envelops galaxies of different types and how together they evolve over cosmic time. We are eager to use the new data coming in to make much stricter tests of theoretical models.” –Molly Michelson

Image: Dark Energy Survey

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