What's NASA Up To And Other Space Stuff

[EyeKhan]

When using starting conditions of an atmosphere and an ocean in simulations of Proxima Centauri B, the likelihood of liquid water and life-sustaining conditions is pretty good. The article calls those starting condition assumptions "reasonable guesses." I don't know enough to judge whether reasonable is the right word. I guess the finding really means that, with all the other conditions (gravity, goldilocks zone location, sunlight), then a liquid ocean and an atmosphere could be sustained, even if the planet is tidally locked...

The Closest Exoplanet to Earth Could Be “Highly Habitable”
A new study suggests Proxima Centauri could sustain liquid water on its surface

Just a cosmic hop, skip and jump away, an Earth-size planet orbits the closest star to our sun, Proxima Centauri.

Ever since the discovery of the exoplanet—known as Proxima Centauri b—in 2016, people have wondered whether it could be capable of sustaining life.

Now, using computer models similar to those used to study climate change on Earth, researchers have found that, under a wide range of conditions, Proxima Centauri b can sustain enormous areas of liquid water on its surface, potentially raising its prospects for harboring living organisms. [9 Strange, Scientific Excuses for Why Humans Haven’t Found Aliens Yet]

“The major message from our simulations is that there’s a decent chance that the planet would be habitable,” said Anthony Del Genio, a planetary scientist at the NASA Goddard Institute for Space Studies in New York City. Del Genio is also the lead author of a paper describing the new research, which was published Sept. 5 in the journal Astrobiology.

Proxima Centauri is a small, cool red-dwarf star located just 4.2 light-years from the sun. Despite its proximity, scientists still know very little about Proxima Centauri’s planetary companion, besides that its mass is at least 1.3 times that of Earth and that it goes around its parent starevery 11 days. Therefore, Del Genio and his colleagues had to make some reasonable guesses about the exoplanet Proxima Centauri b—namely, that it had an atmosphere and an ocean on its surface—for their work to proceed.

Proxima Centauri b orbits in its star’s habitable zone, meaning it’s at just the right distance to receive enough starlight to keep its surface above the freezing temperature of water. But this zone i“ extremely close to the star, Space.com, a Live Science sister site, reported. So it’s likely that the planet has become tidally locked due to gravitational forces. This means that the same side of Proxima Centauri b always faces its parent star, much like how the moon always shows the same side to Earth.

Previous simulations published in a 2016 paper in the journal Astronomy & Astrophysics modeled a hypothetical atmosphere on Proxima Centauri b and suggested that the star-facing hemisphere of the exoplanet might be baked under an intense glare, while a space-facing ocean would be frozen over. Therefore, only a circle of warm sea might exist on Proxima Centauri b—a scenario Del Genio’s team calls “eyeball Earth.”

But the new simulations were more comprehensive than prior ones; they also included a dynamic, circulating ocean, which was able to transfer heat from one side of the exoplanet to the other very effectively. In the researchers’ findings, the movement of the atmosphere and ocean combined so that "even though the night side never sees any starlight, there’s a band of liquid water that’s sustained around the equatorial region," Del Genio told Live Science.

He likened this heat circulation to our own planet’s seaside climates. The U.S. East Coast is balmier than it would be otherwise, he said, because the Gulf Stream carries warm water up from the tropics. In California, by contrast, ocean currents bring cold water down from the North, and the West Coast is colder than it otherwise would be, Del Genio added.

The team ran 18 separate simulation scenarios in total, looking at the effects of giant continents, thin atmospheres, different atmospheric compositions and even changes in the amount of salt in the global ocean. In almost all of the models, Proxima Centauri b ended up having open ocean that persisted over at least some part of its surface.

“The larger the fraction of the planet with liquid water, the better the odds that if there’s life there, we can find evidence of that life with future telescopes,” Del Genio said.

Ravi Kopparapu, a geoscientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in the study, agreed.

“I think it’s exciting that some of these climate outcomes can be observed,” Kopparapu told Live Science. Next-generation facilities, such as the Extremely Large Telescope currently under construction in Chile, might be able to witness heat coming off Proxima Centauri b and differentiate its possible surface conditions, he added.

https://www.scientificamerican.com/a...hly-habitable/

[EyeKhan]

This is pretty cool. The link has some photos from the rovers as they "dropped" to the asteroid's surface. I believe the rovers are going to take samples that will somehow be returned to Earth. It's interesting, this is the second try by JAXA to land on an asteroid and return a sample - the first being only somewhat successful - and it makes me wonder if Japan is pursuing this tech development with dual purpose in mind, science and economic. In other words, are these missions baby steps toward an asteroid mining capability?

In any case, there's gong to be some great stuff from this one I think. Kudos to JAXA!

A Japanese spacecraft just landed two rovers on an asteroid

In a remarkable feat of scientific endeavor, the Japan Aerospace Exploration Agency (JAXA) has successfully landed two small rovers on the surface of an asteroid hundreds of millions of miles from Earth.

“Both rovers … are in good condition,” Japan’s space agency tweeted on Saturday.

<snip>

https://www.yahoo.com/news/japanese-...065500686.html


EDIT:

SciAm just posted an article which speaks to how the sample return will be accomplished. It also says the "mother" craft has two additional landers to deploy. Interestingly, the rovers don't rove, they hop, and each hop lasts about 15 minutes before the craft returns to the surface. Super cool stuff.

Japanese Mission Becomes first to Land Rovers on Asteroid
Twin probes from Hayabusa2 mission have sent back their first pictures from Ryugu’s surface

Japan’s asteroid mission Hayabusa2 has become the first to land moving rovers on the surface of an asteroid.

On 22 September, the Japan Aerospace Exploration Agency (JAXA) tweeted that it had confirmed the mission’s twin rovers, called MINERVA-II 1A and 1B, had landed safely on the space rock Ryugu, and were moving on the surface.

The Hayabusa2 mothership deployed the small probes late last week as it dropped to just 55 metres above the surface, later pulling up to a higher orbit.

Mission controllers at the Japan Aerospace Exploration Agency (JAXA) lost communication with the MINERVA rovers in the hours after deployment. The team said the silence was probably down to the landers being on the far side of the asteroid, as seen from the orbiter.

But the hexagonal rovers have now sent back their first, slightly blurry, colour images of their surface and made their first ‘hop’—their primary means of movement on the rock’s surface. The probes use rotating motors to make jumps, each lasting some 15 minutes owing to the body’s low gravity.

As well as taking images of the asteroid, the landers are designed to measure its temperature.

Before it leaves Ryugu next year, the Hayabusa2 mothership will release two more landers and, in late October, touch the surface itself to collect a sample to bring back to Earth.

Scientists hope that studying the 1-kilometre-wide-asteroid, which is made up of primitive material from the early Solar System, will help them to understand the origins and evolution of Earth and other planets.

This is not the first time scientists have explored an asteroid. In 2005, the mission’s predecessor, Hayabusa, landed on the surface of a smaller asteroid, called Itokawa, and collected a sample that it later returned to Earth. But this is the first time a lander has moved on an asteroid’s surface.

JAXA scientists reported their joy at the rovers’ success. “I cannot find words to express how happy I am,” said Yuichi Tsuda, project manager for the Hayabusa2 mission, in a statement.

This article is reproduced with permission and was first published on September 21, 2018.

https://www.scientificamerican.com/a...s-on-asteroid/

[GGT]

Complicit with the military-industrialized complex?

[Steely Glint]

Space!

[Steely Glint]

https://www.theguardian.com/science/...ine-oort-cloud

Yes! That is top notch thing naming, astronomers.

[EyeKhan]

https://www.theguardian.com/science/...ine-oort-cloud

Yes! That is top notch thing naming, astronomers.

That name's going to stick too. The people that end up settling there in 137 years will be derided as Goblins.

[BalticSailor]

https://www.theguardian.com/science/...ine-oort-cloud

Yes! That is top notch thing naming, astronomers.

https://satwcomic.com/e-elt

[EyeKhan]

This is an interesting idea. Given the rather large, ah, hole in understanding left by the discovery of the universe's accelerating expansion, dark matter and energy and all that goes with it, I rather think some out of the box hypothesizing is in order. It would be delightful for a really unexpected result to come from the observation of Sagittarius A.

Like the article concludes, whatever else happens, I agree the Event Horizon Telescope people will be confused by what they see. (Hardly a daring prediction! )

Are Black Holes Actually Dark Energy Stars?

What does the supermassive black hole at the center of the Milky Way look like? Early next year, we might find out. The Event Horizon Telescope—really a virtual telescope with an effective diameter of the Earth—has been pointing at Sagittarius A* for the last several years. Most researchers in the astrophysics community expect that its images, taken from telescopes all over the Earth, will show the telltale signs of a black hole: a bright swirl of light, produced by a disc of gases trapped in the black hole’s orbit, surrounding a black shadow at the center—the event horizon. This encloses the region of space where the black-hole singularity’s gravitational pull is too strong for light to escape.

But George Chapline, a physicist at the Lawrence Berkeley National Laboratory, doesn’t expect to see a black hole. He doesn’t believe they’re real. In 2005, he told Nature that “it’s a near certainty that black holes don’t exist” and—building on previous work he’d done with physics Nobel laureate Robert Laughlin—introduced an alternative model that he dubbed “dark energy stars.” Dark energy is a term physicists use to describe a peculiar kind of energy that appears to permeate the entire universe. It expands the fabric of spacetime itself, even as gravity attempts to bring objects closer together. Chapline believes that the immense energies in a collapsing star cause its protons and neutrons to decay into a gas of photons and other elementary particles, along with what he refers to as “droplets of vacuum energy.” These form a “condensed” phase of spacetime—much like a gas under enough pressure transitions to liquid—that has a much higher density of dark energy than the spacetime surrounding the star. This provides the pressure necessary to hold gravity at bay and prevent a singularity from forming. Without a singularity in spacetime, there is no black hole.

The idea has found no support in the astrophysical community—over the last decade, Chapline’s papers on this topic have garnered only single-digit citations. His most popular paper in particle physics, by contrast, has been cited over 600 times. But Chapline suspects his days of wandering in the scientific wilderness may soon be over. He believes that the Event Horizon Telescope will offer evidence that dark energy stars are real.

The idea goes back to a 2000 paper, with Evan Hohlfeld and David Santiago, in which Chapline and Laughlin modeled spacetime as a Bose-Einstein condensate—a state of matter that arises when taking an extremely low-density gas to extremely low temperatures, near absolute zero. Chapline and Laughlin’s model is quantum mechanical in nature: General relativity emerges as a consequence of the way that the spacetime condensate behaves on large scales. Spacetime in this model also undergoes phase transformations when it gains or loses energy. Other scientists find this to be a promising path, too. A 2009 paper by a group of Japanese physicists stated that “[Bose-Einstein Condensates] are one of the most promising quantum fluids for” analogizing curved spacetime.

Chapline and Laughlin argue that they can describe the collapsed stars that most scientists take to be black holes as regions where spacetime has undergone a phase transition. They find that the laws of general relativity are valid everywhere in the vicinity of the collapsed star, except at the event horizon, which marks the boundary between two different phases of spacetime.

In the condensate model the event horizon surrounding a collapsed star is no longer a point of no return but instead a traversable, physical surface. This feature, along with the lack of a singularity that is the signature feature of black holes, means that paradoxes associated with black holes, like the destruction of information, don’t arise. Laughlin has been reticent to conjecture too far beyond his and Chapline’s initial ideas. He believes Chapline is onto something with dark energy stars, “but where we part company is in the amount of speculating we are willing to do about what ‘phase’ of the vacuum might be inside” what most scientists call black holes, Laughlin said. He’s holding off until experimental data reveals more about the interior phase. “I will then write my second paper on the subject,” he said.

In recent years Chapline has continued to refine his dark energy star model in collaboration with several other authors, including Pawel Mazur of the University of South Carolina and Piotr Marecki of Leipzig University. He’s concluded that dark energy stars aren’t spherical or oblate, like black holes. Instead, they have the shape of a torus, or donut. In a rotating compact object, like a dark energy star, Chapline believes quantum effects in the spacetime condensate generate a large vortex along the object’s axis of rotation. Because the region inside the vortex is empty—think of the depression that forms at the center of whirlpool—the center of the dark energy star is hollow, like an apple without its core. A similar effect is observed when quantum mechanics is used to model rotating drops of superfluid. There too, a central vortex can form at the center of a rotating drop and, surprisingly, change its shape from a sphere to a torus.

For Chapline, this strange toroidal geometry isn’t a bug of dark energy stars, but a feature, as it helps explain the origin and shape of astrophysical jets—the highly energetic beams of ionized matter that are generated along the axis of rotation of a compact object like a black hole. Chapline believes he’s identified a mechanism in dark energy stars that explains observations of astrophysical jets better than mainstream ones, which posit that energy is extracted from the accretion disk outside of a black hole and focused into a narrow beam along the black hole’s axis of rotation. To Chapline, matter and energy falling toward a dark energy star would make its way to the inner throat (the “donut hole”), where electrons orbiting the throat would, as in a Biermann Battery, generate magnetic fields powerful enough to drive the jets.

Chapline points to recent experimental work where scientists, at the OMEGA Laser Facility at the University of Rochester, created magnetized jets using lasers to form a ring-like excitation on a flat surface. Though the experiments were not conducted with dark energy stars in mind, Chapline believes it provides support for his theory since the ring-like excitation—Chapline calls it a “ring of fire”—is exactly what he would expect to happen along the throat of a dark energy star. He believes the ring could be the key to supporting the existence of dark energy stars. “This ought to eventually show up clearly” in the Event Horizon Telescope images, Chapline said, referring to the ring.

Chapline also points out that dark energy stars will not be completely opaque to light, as matter and light can pass into, but also out of, a dark energy star. A dark energy star won’t have a completely black interior—instead it will show a distorted image of any stars behind it. Other physicists, though, are skeptical that these kinds of deviations from conventional black hole models would show up in the Event Horizon Telescope data. Raul Carballo-Rubio, a physicist at the International School for Advanced Studies, in Trieste, Italy, has developed his own alternative model to black holes known as semi-classical relativistic stars. Speaking more generally about alternative black hole models Caraballo-Rubio said, “The differences [with black holes] that would arise in these models are too minute to be detected” by the Event Horizon Telescope.

Chapline plans to discuss his dark energy star predictions in December, at the Kavli Institute for Theoretical Physics in Santa Barbara. But even if his predictions are confirmed, he said he doesn’t expect the scientific community to become convinced overnight. “I expect that for the next few years the [Event Horizon Telescope] people will be confused by what they see.”

http://nautil.us/blog/are-black-hole...SS_Syndication

[Steely Glint]

Twitter Link

motherfucking space

[EyeKhan]

Okayyyyy... So, changing the outdoor day/night cycle on the proposed scale (i.e rendering streetlights unnecessary for an area up to 50 miles across) is going to wreak ecological havoc on animals and plants, most, if not all, of which take biological and/or behavioral cues from the timing and period of light/ darkness. But... this loony idea is so cool, I really want them to do it just to see what happens.

China wants to put a big fake moon in orbit to reflect sunlight back down at night

The Moon is great, but apparently it’s just not enough for the city of Chengdu in China. Not satisfied with the meager light the Moon reflects back down to Earth at night, scientists in the region plan to launch a satellite that will actually reflect sunlight back down to Earth and turn night into day… sort of.

The satellite is effectively a giant mirror that will redirect sunlight back down on Chengdu even after the Sun sets. The spacecraft will be roughly eight times brighter than the Moon, according to the Chengdu Aerospace Science and Technology Microelectronics System Research Institute, and should provide enough light that it will actually make street lights totally irrelevant for at least part of the city.

If this all sounds kind of bizarre that’s because it is. It really, really is. The group planning the satellite says the mirror will produce light over an area of between 5 and 50 miles. That’s, well, not a very specific, and it’s unclear from current reports just how long the satellite will last.

There’s also been some very real concern that the mirror’s never-ending glow could seriously impact natural cycles of animals. Scientists have long been critical of human light pollution and its ability to potentially throw off the day/night rhythm of animals, and the same could be true of this fake moon plan. Some experts who support the plan suggest that it’ll produce little more than a “twilight glow” that shouldn’t change how animals behave, but nobody will know for certain until the satellite is up and running.

The institute working on the satellite plans to have the fake moon deployed by 2020. There seems to be some conflicting information over just how bright the light will be — something bright enough to make street lights obsolete sure sounds like it’s brighter than a “glow” — so it’ll be interesting to see just how well the mirror works… or doesn’t.

https://www.yahoo.com/news/china-wan...184605929.html

[Cracky]

Such a satellite would have to be enormous. Much bigger than any ever launched.

[Wraith]

Such a satellite would have to be enormous. Much bigger than any ever launched.

It'd be big when its unpacked, but it could be pretty compact when launched.

I'm not really expecting this to happen. China makes a lot of announcements of grand large-scale tech projects, but they always either never materialize or the reality is far less impressive than the claims.

[EyeKhan]

It'd be big when its unpacked, but it could be pretty compact when launched.

I'm not really expecting this to happen. China makes a lot of announcements of grand large-scale tech projects, but they always either never materialize or the reality is far less impressive than the claims.

I don't either. But I really really want them to try!

I wonder how big it would actually need to be? The deliverables are 8X moonlight over a 5 to 50 mile area. Let's call it 20 mile diameter circular area and keep the 8x moonlight. Considering light diffusion, how big does the mirror have to be to end up with a 20 mile wide beam at ground level? I suppose it depends on how high the orbit is - does it have to be geosynchronous - 22k miles - would that dim the light because the orbit is at the equator, or is it so far out, it doesn't really matter much? And considering the intensity of sunlight, how reflective does it have to be to get 8x moonlight at the surface? Is the ideal 100% reflective enough - if not, it's a moot point. Half that acceptable?

Do we have any physicists in the community?

[wiggin]

There were a bunch of scientists interviewed when this story first came out a few days ago. Most of them thought it was technically feasible, though challenging and maybe a bad idea (and probably not a chance it would get done in the timeline).

The moon is pretty darned bright and it's not made of particularly reflective material. Going with a very reflective material that's much closer to the Earth means you can get away with smaller size than might be obvious. There's a lot of engineering details, and I suspect they'd have to think carefully about their fuel costs for stationkeeping (they'd essentially be building a lightsail). But feasible? Probably.

[EyeKhan]

It would make the place a tourist destination, I bet. Nothing else like it in the world.

[EyeKhan]

Sweet photo survey of the ISS found here. Very nice. Need to find higher rez versions for my PC background.

https://spaceflightnow.com/2018/11/0...ions-exterior/

[EyeKhan]

This launch tied SpaceX's record 18 launches set last year. I'm expecting at least one more launch this year to beat that record, maybe more. Looking forward to their attempts to land the second stage. There's been talk, but I haven't seen anything beyond that. I know they've been trying to catch the farings, though with not much success....

A Used SpaceX Rocket Just Launched a Satellite for Qatar, Then Aced a Landing

https://www.space.com/42446-spacex-r...adline+Feed%29

[EyeKhan]

Huh. Looks like SpaceX is giving up on landing the Falcon 9 second stage, directing resources to BFR development instead.

Also, they're getting ready for a first ever 3rd launch of the reusable booster. This will be 2 records - the third use of a booster and 19 launches in one year. I read that the SpaceX goal is to achieve 1 launch/ week, so not quite half way there. I wonder, is there enough business for that rate?

SpaceX Delays Historic Third Launch of Used Rocket (and Its Flock of Satellites)

https://www.space.com/42479-spacex-r...adline+Feed%29

[EyeKhan]

If you're not familiar with the Harvard scientists' argument that Oumuamua is artificial, it's worth reading through this article. To my limited expertise, it's compelling.

I'd welcome any wet blankets from the Wiggin types on the forum.

Because, if this thing actually is artificial, it means one of at least two things: Either the galaxy is so filled with the debris of civilizations that this sort of encounter isn't that uncommon (WOW!), or we just got intentionally scouted by an alien civilization, and all that that implies (Holy Shit!).

Given how odd Oumuamua is, and given there's still a window of time to send a spacecraft for a fly-by, I think we absolutely should do so. Right?

6 Strange Facts about the Interstellar Visitor 'Oumuamua

By Abraham Loeb on November 20, 2018

On October 19, 2017, the first interstellar object, ‘Oumuamua, was discovered by the Pan-STARRS survey. The experience was similar to having a surprise guest for dinner show up from another country. By examining this guest, we can learn about the culture of that country without the need to travel there—a good thing in this case, given that it would take us a hundred thousand years to visit even the nearest star using conventional chemical rockets.

Surprisingly, our first interstellar guest appeared to be weird and unlike anything we have seen before. By the time we realized it, the guest was already out the door with its image fading into the dark street, so we did not have a chance to get a second look at its mysterious qualities. Below is a list of six peculiarities exhibited by ‘Oumuamua:

1. Assuming that other planetary systems resemble the solar system, Pan-STARRS should not have discovered this or any other interstellar rock in the first place. In a paper published a decade ago, we predicted an abundance of interstellar asteroids that is smaller by many (two to eight) orders of magnitude than needed to explain the discovery of ‘Oumuamua, assuming it’s a member of a random population of objects. Put another way, ‘Oumuamua implies that the population of interstellar objects is far greater than expected. Each star in the Milky Way needs to eject 1015 such objects during its lifetime to account for a population as large as ‘Oumuamua implies. Thus, the nurseries of ‘Oumuamua-like objects must be different from what we know based on our own solar system.

2. ‘Oumuamua originated from a very special frame of reference, the so-called local standard of rest (LSR), which is defined by averaging the random motions of all the stars in the vicinity of the sun. Only one star in 500 is moving as slowly as ‘Oumuamua in that frame. The LSR is the ideal frame for camouflage, namely for hiding the origins of an object and avoiding its association with any particular star. The relative motion between ‘Oumuamua and the sun reflects the motion of the sun relative to the LSR. ‘Oumuamua is like a buoy sitting at rest on the surface of the ocean, with the solar system running into it like a fast ship. Could there be an array of buoys that serves as a network of relay stations or road posts, defining the average galactic frame of reference in interstellar space?

3. Most interstellar asteroids are expected to be ripped away from their parent star when they lie in the outskirts of their birth planetary system (such as our solar system’s Oort cloud, which extends to 100,000 times the Earth-sun separation), where they are most loosely bound to the star’s gravity. At these outskirts, they can be removed with a small velocity nudge of less than a kilometer per second, in which case they will maintain the speed of their host star relative to the LSR. If ‘Oumuamua came from a typical star, it must have been ejected with an unusually large velocity kick. To make things more unusual, its kick should have been equal and opposite to the velocity of its parent star relative to the LSR, which is about 20 kilometers per second for a typical star like the sun. The dynamical origin of ‘Oumuamua is extremely rare no matter how you look at it. This is surprising, since the first foreign guest to a dinner party should be statistically common (especially given the larger than usual population inferred in the first point above).

4. We do not have a photo of ‘Oumuamua, but its brightness owing to reflected sunlight varied by a factor of 10 as it rotated periodically every eight hours. This implies that ‘Oumuamua has an extreme elongated shape with its length at least five to 10 times larger than its projected width. Moreover, an analysis of its tumbling motion concluded that it would be at the highest excitation state expected from its tumultuous journey, if it has a pancake-like geometry. The inferred shape is more extreme than for all asteroids previously seen in the solar system, which have an length-to-width ratio of at most three.

5. The Spitzer Space Telescope did not detect any heat in the form of infrared radiation from ‘Oumuamua. Given the surface temperature dictated by ‘Oumuamua’s trajectory near the sun, this sets an upper limit on its size of hundreds of meters. Based on this size limit, ‘Oumuamua must be unusually shiny, with a reflectance that is at least 10 times higher than exhibited by solar system asteroids.

6. The trajectory of ‘Oumuamua deviated from that expected based on the sun’s gravity alone. The deviation is small (a tenth of a percent) but highly statistically significant. Comets exhibit such a behavior when ices on their surface heat up from solar illumination and evaporate, generating thrust through the rocket effect. The extra push for ‘Oumuamua could have originated by cometary outgassing if at least a tenth of its mass evaporated. But such massive evaporation would have naturally led to the appearance of a cometary tail, and none was seen. The Spitzer telescope observations also place tight limits on any carbon-based molecules or dust around ‘Oumuamua and rule out the possibility that normal cometary outgassing is at play (unless it is composed of pure water). Moreover, cometary outgassing would have changed the rotation period of ‘Oumuamua, and no such change was observed. Altogether, ‘Oumuamua does not appear to be a typical comet nor a typical asteroid, even as it represents a population that is far more abundant than expected.

The extra push exhibited by ‘Oumuamua’s orbit could not have originated from a breakup into pieces because such an event would have provided a single, impulsive kick, unlike the continuous push that was observed. If cometary outgassing is ruled out and the inferred excess force is real, only one possibility remains: an extra push due to radiation pressure from the sun. In order for this push to be effective, ‘Oumuamua needs to be less than a millimeter thick but with a size of at least 20 meters (for a perfect reflector), resembling a lightsail of artificial origin. In this case ‘Oumuamua would resemble the solar sail demonstrated by the Japanese mission IKAROS or the lightsail contemplated for the Starshot initiative. An artificial origin offers the startling possibility that we discovered “a message in a bottle” following years of failed searches for radio signals from alien civilizations. Reassuringly, such a lightsail would survive collisions with interstellar atoms and dust as it travels throughout the galaxy.

In contemplating the possibility of an artificial origin, we should keep in mind what Sherlock Holmes said: “when you have excluded the impossible, whatever remains, however improbable, must be the truth.” The Kepler satellite revealed that about a quarter of all the stars in the Milky Way have a habitable planet of the size of the Earth, with the potential to have liquid water on its surface and the chemistry of life as we know it. It is therefore conceivable that interstellar space is full of artificially made debris, either in the form of devices that serve a purpose on a reconnaissance mission or in the form of defunct equipment. However, to validate an exotic artificial origin for ‘Oumuamua, we need more data. As Carl Sagan said, “extraordinary claims require extraordinary evidence.”

In fact, the possibility of a targeted mission adds some explanatory power. It is unlikely that 1015 solar sails are launched per star to make up a random population of ‘Oumuamua-like objects. This would require the unreasonable rate of a launch every five minutes from a planetary system even if all civilizations live as long as the full lifetime of the Milky Way galaxy. Instead, the required numbers could be reduced dramatically if ‘Oumuamua-like objects do not sample all possible orbits randomly but rather follow special orbits that dive into the innermost, habitable regions of planetary systems like our solar system.

‘Oumuamua moves too fast for our chemical rockets to catch up with it now without a gravitational assist from planets. But since it would take ‘Oumuamua thousands of years to leave the solar system entirely, getting a closer look of it through a flyby remains a possibility if we were to develop new technologies for faster space travel within a decade or two. Interestingly, some interstellar objects that pass close to Jupiter can lose energy and get captured by the solar system. These are dinner guests who bumped into a wall on their way out and stayed around after dinner. The Sun-Jupiter system acts as a fishing net. If we can identify trapped interstellar objects through their unusual bound orbits with unusually high inclinations relative to the solar system plane, we could design missions to visit them and learn more about their nature.

Alternatively, we can wait for the next interstellar guest to show up. Within a few years, the Large Synoptic Survey Telescope (LSST) will become operational and be far more sensitive to the detection of ‘Oumuamua-like objects. It should therefore discover many such objects within its first year of operation. If it does not find any, we will know that ‘Oumuamua was special and that we must chase this guest down the street in order to figure out its origin.

Studying interstellar objects resembles my favorite activity when walking along the beach with my daughters. We enjoy picking up seashells that were swept ashore and learning about their different origins. Every now and then, we find a plastic bottle that indicates an artificial origin. Similarly, astronomers should examine any object that enters the solar system and study its properties. There is no doubt that the six peculiar features of ‘Oumuamua have the potential to usher in a dramatic new era in space science.

https://blogs.scientificamerican.com...itor-oumuamua/

[Aimless]

That is a list of compelling arguments for why Oumuamua is unusual and should be studied if possible—neither more nor less. The first part consists of some pretty tenuous inferences afaict. But yes, we should pursue

[EyeKhan]

That is a list of compelling arguments for why Oumuamua is unusual and should be studied if possible—neither more nor less. The first part consists of some pretty tenuous inferences afaict. But yes, we should pursue

They are not arguments for why it's unusual - they are the facts that make it unusual. They are arguments for why somebody should spend a few bucks to go take a close look at it.

Oh, and it's a fucking alien probe and now that they've taken a closer look at us, we are clearly....? What? Quarantined, most likely, because, you know, we're a cluster fuck. Unless they're xenophobes, and in that case we'll be scheduled for elimination, because, you know, we're a possibly dangerous cluster fuck. I doubt any aliens would bother trying to talk to us, and the idea of invasion is just stupid.

[Wraith]

If it is a probe, that's a pretty fucking big time scale the aliens are operating on.

[BalticSailor]

As for the No 1 on that list, I don't quite understand how they can imply anything about the population of such objects from a single data point.

[wiggin]

Baltic, I think the theory is that they have a model about how often objects of this size/etc. are ejected from a system, and based on the length of time we've been observing, seeing something this big is either incredibly unlikely to happen naturally or maybe it wasn't natural. The big problem with their reasoning is twofold:

First, they pay lip service to the idea that their model is wrong, but they jump pretty quickly to an explanation of deliberate action when - let's be honest - it's far more likely that our understanding of how star systems is incomplete than it is that an alien probe happened to whizz through our system just when we start noticing. Second, there's stretching some very thin data into a very big story. The fact of the matter is that all of this data is a single pixel on a telescope that's varying position and brightness. You can learn a lot about an object from this kind of information, yes, but even the estimates for things like size and aspect ratio have pretty big uncertainties. A lot of their analysis rests on certain assumptions about where in that range the object actually fits. Lastly, they make a big case of this being a 'stealth' probe that masks its origin intentionally by being relatively motionless wrt the local frame of reference. But a much simpler explanation is that it was just ejected a really long time ago, which has given it time to reach that state naturally.

Might it be worth a look just for scientific curiosity? Sure! Is it technically feasible? Probably not. The crazies who tried to figure out whether it was feasible suggested building an entirely new vehicle combining a number of different technologies to just get close to the rock... and launching by 2021. It ain't happening.

[Wraith]

As for the No 1 on that list, I don't quite understand how they can imply anything about the population of such objects from a single data point.

Almost all naturally occurring properties can be arranged in a Gaussian distribution. We don't necessarily know what that curve looks like, but it's going to be big in the middle and small on the sides. So if you pick one object at random from that group of things, you're more likely to be getting an item from the middle. You're most likely to get the object that is perfectly average. So even when you only have one data point, you can still know that you most likely have something within 1 standard deviation of the mean, and almost certainly have something within 2 standard deviations of the mean. It's possible it's further away, but if you just assume you're within 2 standard deviations you'll be right 19 times out of 20. You still don't get an idea of what a standard deviation is or even which side of the mean you're on, but it gives a good starting point for what you should expect to see lots more of.

This works with the number of times something should occur, too. So if we spend 5 years looking for a thing before we find the first one, we can safely assume that 5 years is within two standard deviations of the average amount of time it'll take to find another of those things the way we're doing it. We also have a nice lower bound since you can't take less than 0 time to find something, so that gives us a bounds for what the standard deviation will most likely look like.

In this case specifically, we found this faster than our models said we should have. So either our models are wrong, we just experienced a lottery-winning low-probability event, or this isn't part of the natural phenomena that we modeled. And, comeon, isn't it more fun to think about what it would mean if it's from outside our model, instead of just going with 'our models are wrong'?

Fun fact: If you take all natural phenomena that can be fit to a Gaussian distribution, and measure how far they deviate from ideal form of one, those measurements will form a Gaussian distribution.

[Steely Glint]

Baltic, I think the theory is that they have a model about how often objects of this size/etc. are ejected from a system, and based on the length of time we've been observing, seeing something this big is either incredibly unlikely to happen naturally or maybe it wasn't natural. The big problem with their reasoning is twofold:

Three; the same reasoning applies to the alien probe hypothesis, based on the length of time we've been observing, Earth must be constantly getting buzzed by alien probes (in which case, why the... *gestures at a seemingly completely empty galaxy*) or we just witnessed something incredibly unlikely. Either way, we just witnessed something incredibly unlikely, so the alien probe theory doesn't even get rid of that.

And, you know, if there are a thousand possible outcomes to an even each equally likely in probability then whatever happened you get to say you just witnessed something incredibly unlikely... but you don't get to say aliens did it.

[EyeKhan]

Three; the same reasoning applies to the alien probe hypothesis, based on the length of time we've been observing, Earth must be constantly getting buzzed by alien probes (in which case, why the... *gestures at a seemingly completely empty galaxy*) or we just witnessed something incredibly unlikely. Either way, we just witnessed something incredibly unlikely, so the alien probe theory doesn't even get rid of that.

And, you know, if there are a thousand possible outcomes to an even each equally likely in probability then whatever happened you get to say you just witnessed something incredibly unlikely... but you don't get to say aliens did it.

Does it change anything if the aliens sent the probe here intentionally, rather than a random flyby? Random means there's a zillion probes out there, but if the aliens are specifically interested in Earth, then it means something entirely different, possibly.

By intent, I'm thinking the Earth has had life, and the atmosphere has shown signs of that life, for 3 billion years +/-. We ourselves are on our way to being able to identify life signatures in exoplanet atmospheres via telescope, so, it's reasonable to assume any relatively nearby aliens with similar interests identified life here a very long time ago. Perhaps they fire off a probe periodically to do flybys, maybe 1 every 3.76 years, and have been doing it for 100 million years. Does 3 billion years or so of being discoverable change the math at all?

[Steely Glint]

Does it change anything if the aliens sent the probe here intentionally, rather than a random flyby? Random means there's a zillion probes out there, but if the aliens are specifically interested in Earth, then it means something entirely different, possibly.

By intent, I'm thinking the Earth has had life, and the atmosphere has shown signs of that life, for 3 billion years +/-. We ourselves are on our way to being able to identify life signatures in exoplanet atmospheres via telescope, so, it's reasonable to assume any relatively nearby aliens with similar interests identified life here a very long time ago. Perhaps they fire off a probe periodically to do flybys, maybe 1 every 3.76 years, and have been doing it for 100 million years. Does 3 billion years or so of being discoverable change the math at all?

1) If there are any 'relatively nearby aliens' then the galaxy must be absolutely teeming with advanced civilisations, otherwise we're looking down the barrel of another absolutely enormous coincidence, far bigger than either the random bit of rock or random alien probe ones. And the galaxy isn't teeming with advanced civilisations.
2) As Wraith pointed out, 'Oumuamua is slow. It is, in fact, only travelling twice as fast as Voyager, which was never even intended as an intersteller probe. So if these hypothetical aliens have been space faring for 100 million years and still can't make better probes they need to ask themselves some questions. You could colonise the galaxy a few times over in that timescale.

[EyeKhan]

1) If there are any 'relatively nearby aliens' then the galaxy must be absolutely teeming with advanced civilisations, otherwise we're looking down the barrel of another absolutely enormous coincidence, far bigger than either the random bit of rock or random alien probe ones. And the galaxy isn't teeming with advanced civilisations.
2) As Wraith pointed out, 'Oumuamua is slow. It is, in fact, only travelling twice as fast as Voyager, which was never even intended as an intersteller probe. So if these hypothetical aliens have been space faring for 100 million years and still can't make better probes they need to ask themselves some questions. You could colonise the galaxy a few times over in that timescale.

Referring to the numbers:
1) We don't know, yet, the galaxy isn't teaming with advanced civilizations. This could be our first solid clue it is, which is why it's such a curiosity...

2) The hundred million years is just a for instance. And I don't think the speed of the object, slow as it is, necessarily says anything definitive, given the huge scope of the unknowns we are facing.

I doubt very much there will be any chance to send a spacecraft to take a look at it, which is unfortunate. But it would be worth considerable expense, imho, given how odd the object appears to be.

[Steely Glint]

Referring to the numbers:
1) We don't know, yet, the galaxy isn't teaming with advanced civilizations. This could be our first solid clue it is, which is why it's such a curiosity...

2) The hundred million years is just a for instance. And I don't think the speed of the object, slow as it is, necessarily says anything definitive, given the huge scope of the unknowns we are facing.

I doubt very much there will be any chance to send a spacecraft to take a look at it, which is unfortunate. But it would be worth considerable expense, imho, given how odd the object appears to be.

1) We kind of do know that, though. With 13 billion years to play with the sky should be absolutely riddled with alien crap by this point if life is so common in the universe that two technological civilisations developing within, say, a thousand light years of each other isn't a ridiculously huge coincidence, and yet we can't find anything. In my personal view, our very existence demonstrates the extreme rarity of life, it is very unlikely that a planet as kushy as Earth would have been left alone while it was in the single cell sludge stage (which it was for the majority of it's history) would have been left alone in a universe with thousands or millions of advanced civilisations running around for millions or billions of years.
2) I actually think the speed of the object rules out it having been deliberately sent all by itself. You wouldn't send something that's going to take a million years to get to where you want to go when you can just wait for technology to advance a bit and then get there in a few hundred or thousand, or shorter.

I honestly think it's more likely that I'm an alien probe than Oumuamua.