Almost all the links this month are space related. I promise I spend time thinking about other things but…there’s just a lot of cool space-related links on the internet.
Video of the night sky with the stars stabilized so you can watch the ground spin around.
- For several years the ESA worked on a spacecraft that would test the idea of deflecting a comet with a high-speed impactor. It was brilliantly named Don Quijote, with the rash impactor craft “Hidalgo” rushing in to the target with the observation craft “Sancho” watching from a safe distance. Unfortunately, it looks like the project stalled years ago, but a proposed joint NASA-ESA mission Asteroid Impact & Deflection Assessment (AIDA) could carry the torch [PDF] by targeting the asteroid 65803 Didymos. Didymos is actually a binary system, with a large primary asteroid and a smaller secondary asteroid orbiting it. When the impactor strikes the primary (speed ~ 6.25 km/s), it would induce perturbations to the orbit of the secondary observable from Earth. A 2019 launch and 2022 impact date have been chosen so that Didymos will be passing close to the Earth and the impact event will be visible to ground-based radar.
Half of all stars are not in galaxies?
Astronomers have spotted a faint cosmic glow, unseen until now, that may come from stars that float adrift between galaxies. The discovery suggests that as many as half of all stars in the Universe lurk outside galactic boundaries….The stars were probably tossed there when galaxies collided.
I don’t understand how this is still uncertain given our knowledge of galaxy and structure formation. But in any case, it’s interesting to note that the large majority (>85%) of all the stars we see in the night sky are within 1,000 light years of Earth. You could guess this from the fact that the Milky Way is disk is about ~1,000 light years thick and ~100,000 light years in diameter. If we could easily see stars further than the thickness, then we’d see a lot more stars along the Galactic disk. But instead, the only sign of the disk is the diffuse glow, giving the Milky Way it’s name, of very distant, undifferentiated stars.
Stars outside of galaxies would be at much lower density, so anyone on a planet orbiting such a star wouldn’t see hardly any points of light in the sky. If most such stars are still within the Galactic groups, then they would probably just see faint smudges of other galaxies like the very dim Magellanic Clouds we can see.Note that these are still pretty big, though, in terms of angular size. Several moons wide. a On the other hand, lone stars in voids away from Galaxy clusters would presumably have nothing visible at all to the naked eye.
Scott Manley on the feasibility of gun launched space missions:
Scott Manley with a pretty visualization of the history of asteroid discovery:
It’s a common misconception that low-Earth orbit is hard to get to because it’s high up, when really most of the difficulty comes from how fast (horizontally) you need to get going. This leads folks to wonder if astronauts could just parachute out of the ISS back to Earth, or wonder why high-altitude skydivers like Alan Eustace don’t experience the extreme heating of atmospheric re-entry.
But what would it take for an astronaut to return from low-Earth orbit without a space craft? Enter Man Out Of Space Easiest (MOOSE):
The system was quite compact, weighing 200 pounds (90 kilograms) and fitting inside a suitcase-sized container. It consisted of a small twin-nozzle rocket motor sufficient to deorbit the astronaut, a PET film bag six feet (1.8 metres) long with a flexible quarter-inch-thick ablative heat shield on the back, two pressurized canisters to fill it with polyurethane foam, a parachute, radio equipment and a survival kit.
The astronaut would leave his vehicle in a space suit, climb inside the plastic bag, and then fill it with foam. The bag had the shape of a blunt cone, with the astronaut embedded in its base facing outward. The rocket pack would protrude from the bag and be used to slow the astronaut’s orbital speed enough so that he would reenter Earth’s atmosphere, and the foam-filled bag would act as insulation during the subsequent aerobraking. Finally, once the astronaut had descended to 30,000 feet (9 km) where the air was sufficiently dense, the parachute would automatically deploy and slow the astronaut’s fall to 17 mph (7.6 metres per second). The foam heat shield would serve a final role as cushioning when the astronaut touched down and as a flotation device should he land on water. The radio beacon would guide rescuers.
Documentary style video on Soyuz undocking, reentry, and landing:
- The MESSANGER spacecraft is nearing the end of its life. It has been in orbit around Mercury (the first probe to do so) for 3 years, fulfilling its primary mission, but it is running low on the propellant that is needed to keep its orbit from decaying.This is due to perturbations from the nearby sun, not the (essentially non-existant) Mercurian atmosphere. b It is expected to crash into the surface of the planet some time in March. NASA will keep collecting imagery and other data right up until its demise and, since no probe has yet landed on the planet, the last pictures will be the highest resolution ever. Unfortunately MESSANGER must transmit all of its photos itself back to earth (since it has no companion) and the last photos that will be available depend on exactly where the spacecraft is in its orbit, and how Mercury is oriented at that time with respect to Earth. Although it will take some luck, there is a chance that MESSANGER will take high-resolution “before” photos of its own impending crash site — wherever that turns out to be — and that “after” photos could be taken by the ESA spacecraft BepiColombo, which arrives in 2024.
The long-term scientific roadmap Enduring Quests-Daring Visions (NASA Astrophysics in the Next Three Decades) contains a sketch of an ambitious but physically plausible telescope array for directly imaging exoplanets:
A large optical/near-IR space-based interferometer would spatially resolve nearby habitable planets, delivering multicolor images and even spectra over the face of a potentially or known lifebearing planet. Ultimately, this kind of information will be crucial for analyzing and understanding evidence for life, since, for example, finding biosignatures that are identified with land features, or a chlorophyll-like feature (“red edge”), could be decisive evidence for advanced life—beyond the single-cell phase that occupied a large fraction of Earth’s history. To fully exploit this capability, the facility would have to be sufficiently large to produce such measurements in only a few hours of integration, since rotation of the planet will (over longer observation times) dilute such signatures. While such a challenging mission is clearly beyond the 30-year timescale, it appears more feasible than travel (manned or unmanned) to other habitable planets, and is, therefore, the most credible option to map the surfaces of habitable planets. There are three fundamental parameters for a multitelescope interferometry facility: the maximum separation between the telescopes, the total light collecting area of the telescopes combined, and the number of individual telescopes. For the notional architecture described here, we assume a goal of a 30 × 30 element map at optical wavelengths (0.3 to 1 micron) of an Earth located 10 parsecs (33 light-years) away. To achieve the needed spatial resolution at all wavelengths, the maximum separation between the telescope units must be ~ 370 kilometers. A total collecting area of around 500 square meters will provide the sensitivity required for R ~ 100 spectroscopy of every spatial element within a day of exposure time. The number of individual telescopes needed depends on the exact details of the observations and observing strategy, but not more than 20 units will be necessary. In this case, each telescope unit would need to have a diameter of ~ 6 meters (larger if fewer telescopes are used). Other architectures capable of achieving our science goals could be envisaged, but the above provide a sense of the technical challenges involved.
- Scott Aaronson lists some peculiarities of the plot of Intertellar.
Quanta has an article on the difficulty of testing various explanations for why sexual reproduction is so overwhelming in the animal kingdom.
This is closely related to a question I’ve often asked but have only heard even acknowledged a couple of times (at least in terms I could recognize), much less answered: Why is sexual dimorphism so mild? Males and females have some drastically different requirements and selective pressures; if two isolated population had such different pressures, we’d definitely expect them to diverge into very different species. The most notable difference is that for the large majority of animals only females are needed to carry developing offspring to term, and lots of other sex difference arise from this: high-risk/high-reward strategies severely limited for females; during sex selection, males may be judged more on gene quality than actual health; different mate-guarding strategies; and so on.
Yes, we document lots of small ways they are different, but why don’t males and female look like different species on macroscopic scales? (At the cellular level, it seems more natural that they should have to be very similar.) Why aren’t there animal species where the females live underwater and males live on ground? Why don’t many more animals feature sexual dimorphism as extreme as the Angler fish?
A reasonable guess is that it has to do with the fact that males and females share almost all their chromosomes, but naively this doesn’t seem like much of a restriction since large dimorphisms could be described on non-sex chomosomes but only triggered by sex-chromosome controlled hormones, just like there are dramatic age-related changes as individuals of a species develop.
EDIT: Twitter is aflutter with Musk’s announcement of drone sea landing barges. I’m not really sure why the autonomous part is so important, but what I was excited to find out is that the first stage of the December 16 SpaceX launch of CRS-5 will try to land on the barge. Musk laid out the odds:
If the stage successfully lands on the platform, Musk said, it could potentially fly again. He put the odds of success at no greater than 50 percent for this particular attempt, but was more optimistic about the company’s chances of landing on the platform on a future mission.
“There’s at least a dozen launches that will occur over the next 12 months,” Musk said. “I think it’s quite likely — probably 80 to 90 percent likely — that one of those flights will be able to land and refly.”