Archive for the 'Astronomy' Category

Oct 25 2019

Mystery of the Hubble Constant

Published by under Astronomy

76.8 kilometers per second per megaparsec.

A megaparsec is about 30 million trillion kilometers, or perhaps better stated as 30 exameters. Given the significant figures, and the massive denominator, that makes this constant extremely precise. But is it accurate? Other measures using different methods come up with 74.03, 71.9, 69.8, and even 67.4.

We are talking about the Hubble constant, the rate of expansion of the universe. Edwin Hubble first proposed that the entire universe is expanding in 1929. This was based initially on observations by Harlow Shapley that other galaxies appear to be moving away from us. Their color is red-shifted from the doppler effect on the light coming to us from those galaxies. (As an aside, this applies to galaxies outside our local galaxy cluster, which are not uniformly moving away from us because we are gravitationally bound.) Hubble then made an extensive measure of the red shift of galaxies, and found that the farther away galaxies were, the more red shifted they were. This could be explained if the entire universe were expanding.

In 2011 three astrophysicists were awarded the Nobel prize for their discovery that, no only is the universe expanding, this expansion is accelerating. This means there must be an unknown force overcoming gravitational attraction and pushing everything apart – a force now called dark energy. But dark energy is not the mystery I am referring to in the title.

The mystery of the Hubble Constant is why different astronomers and different methods come up with different numbers? There are a few generic possibilities here – whenever different measurements disagree. It’s possible that the measurements themselves are simply inaccurate. This is always the first assumption and needs to be explored and ruled out before other explanations are seriously considered.

What generally happens is as more and more careful and thorough measurements are made, or the techniques or instrumentation are refined, the measurements start to converge on the real answer. Problem solved. However, that is not what is happening with the Hubble Constant. It is perhaps too early to tell for sure, but so far measurements have not been steadily converging. This, in fact, is essentially the mystery.

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Oct 08 2019

2019 Nobel Prize in Physics Goes To Three Astronomers

Published by under Astronomy

It’s Nobel Prize time of year again (it always seems to come around so fast), and the Nobel Prizes for Medicine and Physics have been announced. The physics prize goes to three astronomers, James Peebles, Michel Mayor and Didier Queloz, for contributing to our understanding of the universe and our place in it.

This is a more abstract Nobel Prize theme than many, and the first awardee, James Peebles, was recognized for a lifetime of collaborative research, more than any specific discovery. I like it.

Peebles was one of the cosmologists who predicted the existence of the cosmic microwave background radiation (CMB). This is the afterglow of the Big Bang at the beginning of our universe. It’s existence was confirmed in 1964 by astronomers Robert Wilson and Arno Penzias. It’s hard to overstate how monumental this prediction and later confirmation were to cosmology and our understanding of the universe.

The utility of the CMB goes beyond confirming the Big Bang. As the name implies, it is now the background temperature or glow of the entire universe. This has proven to be a highly useful window into the history and structure of the universe. Everything on the cosmic scale seems to leave its fingerprints in the CMB. That is always the best kind of discovery, and I have noticed one that attracts the attention of the Nobel committee – discoveries that open up entire fields of subsequent research.

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Oct 04 2019

Mission To Find Life On Mars

Published by under Astronomy,Technology

The next NASA rover to Mars, the Mars 2020 Rover (final name to be determined), launches next July. It will arrive at Mars in February 2021. This is the next iteration of rover design and has some interesting new features, include a drone that can fly around to survey more of the Martian surface.

But perhaps the feature that is getting the most attention is the drill. For the first time a Mars rover will have the ability to drill down into the rock and dirt. Why is this so important? If Mars ever contained life, then it is likely the remnants of that life can be found down in the rocks, rather than on the surface. This is the first rover specifically designed to look for signs of life.

There is even the remote possibility of finding signs of recent, or even current life. The mission will be looking for life signatures, such as certain forms of carbon, or signs of sustained water presence in the past. Once the rover lands and is operational, it should only take a few months for answers to start beaming to life. We may know by the middle of 2021 if life ever existed on Mars.

Finding signs of life on Mars will have profound scientific implications. However, CNN, when reporting about this, chose to go with this headline: “When — or if — NASA finds life on Mars, the world may not be ready for the discovery, the agency chief says.” They quotes NASA chief scientist, Jim Green:

“It will be revolutionary,” Green told the Telegraph. “It will start a whole new line of thinking. I don’t think we’re prepared for the results. We’re not.”

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Sep 19 2019

Potential Second Interstellar Object

Published by under Astronomy

In 2017 astronomers detected and confirmed the first interstellar object, an asteroid from another solar system racing through our own – Oumuamua. The object is long and thin, like a cigar, and appears to have some outgassing altering its trajectory. So it’s not quite a comet, but not just a rock either. We didn’t detect Oumuamua until after it has passed by its closest approach to the Earth. It whipped around the sun and is now heading up out of the plane of our solar system.

We know Oumuamua is an interstellar object because it is going very fast and is on a trajectory that is not bound to the sun. There are two interesting aspects to Oumuamua. The first is that it is changing course slightly, as if it is outgassing, but we don’t see the outgassing. It is not a regular comet. The second is that its course was aimed, on a cosmic scale, right at the sun. If you look at the path (below) and extrapolate out to interstellar distances, that is a phenomenal bullseye. If you do the math, and one astronomer did, the probability of such a close encounter with an interstellar object is 100 million to one.

Oumuamua came within 0.25 AU of the sun and 0.15 AU of the Earth. If this were random, they calculate that stellar systems on average would have to eject 10^15 such objects – which is 100 million times more than projected. That means that our chance encounter with Oumuamua was a 1 in 100 million chance – that’s like winning the interstellar lottery. This lead that astronomer to speculate that perhaps Oumuamua is not a random asteroid, but a ship that was aimed at our sun. Perhaps solar sails explain the course change without visible outgassing.

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Jul 26 2019

Going Back to the Moon

Published by under Astronomy,Technology

With the 50th anniversary of Apollo 11 landing on the moon there has been a lot of talk about NASA’s plans to return. Each new dribble of news can be exciting, but a coherent plan remains elusive. Somewhat of a plan is starting to take shape, however.

In a recent commentary for the Washington Post, Astronomer Phil Plait made an interesting point – that the Apollo mission was designed to be self-limited and not a sustained effort. The point was to beat the Soviets to the moon, and so it was baked into the design of the program to do everything to get their quickly not slowly and sustainably. Further, once we did beat the Soviets to the moon, and it was clear they abandoned their own efforts to do so, support for the program faded.

I think this is correct, but it is in contrast to the naive impression I formed as a child during the Apollo program and nurtured throughout most of my life. It always seemed to me that once we became a spacefaring race, progress was inevitable. Certainly every science fiction movie reinforced this impression. Apollo was followed by the space shuttle, then the ISS. OK, that makes sense. But then progress in sending people into space seemed to wane. We now have to hitch rides to the ISS on Russian craft. NASA’s plans seem to change with each administration. Multiple conflicting visions compete for dominance, while we seem to chase our tail.

I have to now acknowledge that it’s possible the massive effort necessary to safely send people to the moon and return them to Earth may only be feasible with the political and public support generated by the cold war and an immediate space race. Without that, we don’t seem to be able to sustain the political will – which in practical purposes means money. NASA and the White House need to be on the same page, and Congress needs to provide the funding.

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May 20 2019

New Probe To Look For Life On Mars

Published by under Astronomy

One of the greatest scientific questions to remain unanswered so far concerns the existence of life outside of the Earth. So far the only place in the universe where life has been confirmed in on Earth itself. There is almost certainly life elsewhere, the universe being as big as it is, but we have not confirmed it.

Looking in other stellar systems will not be easy. We will not be traveling to any other stars anytime in the foreseeable future, so what are the options for probing for extrasolar life? We can look for the chemical signatures of life in the atmosphere. Or we can try to detect signals from a technological species. That’s pretty much it at this point, unless that life brings itself or its probes to us.

Our best bet to detect life off Earth, therefore, is to look within our own solar system. There are really only a few plausible locations for life – in the oceans beneath Europa or Enceladus, in the atmosphere of Jupiter or one of the other gas giants, or on Mars. No where else has plausible conditions for life.

Of these possibilities, Mars is the easiest to get to. We have already landed a number of probes on Mars. None of these robots, however, have been equipped with the necessary tools to directly look for life. They did examine the conditions on Mars which could potentially inform the probability of life on Mars, but that’s it. The bottom line of this examination is that conditions are not particularly suited for life as we know it, but does not exclude the possibility of life.

One interesting find is the presence of perchlorates at 0.5-1% in Martian soil, likely widely distributed around the planet. These are reactive molecules containing oxygen, and present both good and bad news for human intentions on Mars.  The bad news is that perchlorates are toxic, and any human presence on Mars will have to deal with the soil itself being a hazard. Extreme measures will be needed to protect astronauts. This is not a deal-killer, but it is a significant technical hurdle.

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May 02 2019

Pilots Reporting UFOs

The Navy recently drafted new policies for how its pilots and other personnel should report any encounters with “unexplained aerial phenomena” – more commonly known as unidentified flying objects, or UFOs. They say this is in response to an uptick in pilots reporting such encounters and requesting a formal way to report them.

The reporting on this topic ironically reveals the underlying problem in the first place – there is a stigma attached to the reporting of UFOs because of their cultural association with claims that they are (or may be) alien in origin. People mentally equate UFO with flying saucer (a colloquial term for any alien spacecraft of any shape).

Even sober takes on this topic focus heavily on the probability that such sightings are an alien phenomenon. Tyler Cowen does touch on many possible interpretations of UFO sightings, but spends the bulk of his commentary exploring how probable it is that aliens are visiting. He concludes it is not likely, but the chance is non-zero and deserves to be explored.

While I basically agree, I still think the framing is problematic. Essentially we are taking a phenomenon that likely has multiple causes, some known and some unknown, and focusing most of our attention on what is probably the least likely unknown possible cause. This would be like defining a new clinical syndrome by the least likely possible disease that could be causing it. This constrains our thinking, and in this case creates an unfair stigma. It also fuels conspiracy theories and wild speculation by the public. An further, it has resulted in paying too little attention to a phenomenon that may have practical real-world implications.

Returning to the medical analogy – there are fake diseases in the popular culture used to explain very real symptoms. For example, some people with chronic skin symptoms think they have a bizarre form a parasitosis. They clearly don’t, but that should not cause us to be dismissive of everyone with the same symptoms, or to ignore the search for underlying real causes.

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Nov 05 2018

Oumuamua and the Alien Hypothesis

Published by under Astronomy

One year ago, in October 2017, astronomers detected the first confirmed interstellar visitor to our solar system – an asteroid dubbed Oumuamua. The name is Hawaiian for “scout”, as if the asteroid is a messenger from a distant system. A Hawaiian name was chose because the object was discovered by the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) in Hawaii. Determining that Oumuamua was an interstellar object was not difficult – the determination was based on its trajectory. It was traveling really fast, too fast for any object originating from our own system. It’s velocity would also take it out of our system – it was moving too fast to be captured by the gravity of our sun.

All of that is cool enough, but astronomers carefully analysing the trajectory of Oumuamua discovered (and published their findings in June 2018) that its acceleration could not be explained entirely by gravity. Some force was pushing, ever-so-slightly, on the object. This acceleration could be explained by outgassing, if there were any volatiles on Oumuamua that were heating up as it got closer to the sun. These gases would be like tiny rocket engines. Observations of the object did not detect any comet-like tail, which is why it was thought to be an asteroid. But if this new observation were correct, then it would have the ices and gases associated with a comet.

Oumuamua was discovered 40 days after its closest approach to the sun, when it was already on its way out of our solar system. At this point it should have been slowing down a bit from the pull of the sun’s gravity, but instead it was speeding up slightly. This could be explained by outgassing caused by heat from the sun.

This led to a debate about whether or not Oumuamua was an asteroid with a small amount of ice, or a comet that had lost most of its ice. It seems that the object exists in the gray zone between asteroid and comet (and we run into yet another definition demarcation problem). Further, close analysis showed that Oumuamua is very elongated (often described as “cigar-shaped”) and quickly tumbling end-over-end.

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Sep 28 2018

Alien Technosignatures

I have long maintained that one of the greatest scientific questions for humanity is – are we alone in the universe? How common is life, and how common are alien technological civilizations? When we finally reach out into space, will it be empty for us to inhabit, or will we quickly encounter a galactic civilization? What will alien intelligent species be like, and what will that tell us about ourselves?

It is unfortunately likely that we will not have any real answers to any of these questions anytime soon. But that does not mean we shouldn’t look. Recently NASA held a workup to explore possible avenues of looking for alien technosignatures – signs of advanced alien civilizations that we can see from Earth. Some of the participants also held a Reddit AMA.

So – what are alien technosignatures and how can we find them?

The most basic type is radio signals. There has been an effort to listen for alien radio signals for decades, often referred to as SETI, the Search for Extraterrestrial Intelligence. The idea is that radio signals are a convenient way to communicate across lightyears, and perhaps an alien world is sending out such signals for others to find. But really, we have been looking for radio signals because we can. It’s like the person looking for a lost item under a lamp post, not because they have any reason to find it there, but because the light is good.

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Sep 11 2018

The Pluto Debate Rages On

Published by under Astronomy

If you have not watched Rick and Morty, I highly recommend it. It is an adult-themed cartoon, very entertaining, and extremely well written. On one episode Jerry, while trying to help his son Morty with a science project, mistakenly says that Pluto is a planet. When Morty corrects him, Jerry doubles-down and will not relent, going as far as to call NASA to insist that Pluto be reclassified a planet. This gets the attention of the Plutonians, who are themselves engaged in a raging controversy over whether or not Pluto is a full planet, and who enlist Jerry as an “Earth scientist” to support the planet position. This plot line is really a commentary on science denial, specifically global warming denial.

The Pluto controversy back on Earth is less intense, and the stakes are lower, but it remains and interesting debate about how to optimally categorize things in science. What categories should we have, and what criteria should we use? Should scientific utility be the only measure, or should public understanding also play a role?

Pluto was discovered in 1930 by Clyde Tombaugh and was designated as the ninth planet. Pluto has always been, for some reason, a popular favorite, maybe because of the name, maybe because it was the smallest planet. Pluto has the most eccentric orbit of any of the classic 9 planets, and it’s orbit actually crosses over the orbit of Neptune. It is also the first Kuiper belt object discovered – a region of our solar system beyond Neptune that is full of icy objects.

Problems started for our nice planetary system when other Kuiper belt objects started to get discovered. In 2005 Eris was discovered – it is slightly smaller than Pluto but is 27% more massive (because it is more dense). Eris also has a moon, Dysnomia. Two other large Kuiper belt objects have since been confirmed and named – Makemake and Haumea.

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