Archive for the 'Astronomy' Category

Sep 15 2020

Life on Venus?

Published by under Astronomy

This is definitely the big news of the week – scientists have detected phosphine gas in the clouds of Venus. This is a big deal because phosphine gas is a potential marker for life. This adds Venus to the list of worlds in our solar system that are candidate hosts of life, along with Mars, Europa, Enceladus and others. Europa and Enceladus are moons with an icy shell and definitely liquid water underneath. The presence of liquid water is what makes them intriguing candidates for potential life. Mars is currently dry and desolate, but in the past was warmer and wetter. Life could have evolved on Mars, and we may find the fossil evidence of such life. Or, unlikely but possible, life could have barely clung to some ecosystems in the Martian soil.

But Venus was not a serious contender for life, and least not after we sent probes there. Prior to the first probe in 1962 scientists and science-fiction writers fantasized about life on Venus. It is our nearest neighbor, almost the same size as Earth, and all those clouds might contain water vapor. Perhaps Venus was a jungle planet. But now we have sent multiple probes to map the planet, and Soviet probes even landed on Venus (surviving for only a short period of time). Here is NASA’s summary of the planet:

Venus has a thick, toxic atmosphere filled with carbon dioxide and it’s perpetually shrouded in thick, yellowish clouds of mostly sulfuric acid that trap heat, causing a runaway greenhouse effect. It’s the hottest planet in our solar system, even though Mercury is closer to the Sun. Venus has crushing air pressure at its surface – more than 90 times that of Earth – similar to the pressure you’d encounter a mile below the ocean on Earth.

Crushing heat, gravity, and sulfuric acid do not make for a hospitable world. However, hope for life on Venus was never completely abandoned. Optimists pointed out that in the upper atmosphere of Venus there is a sweet spot where the temperatures are warm and comfortable for organic reactions and the pressure would be less. Sure, there would still be an acidic atmosphere, but there are extremophiles on earth that thrive in high acidity (acidophiles). I don’t think this was considered a high probability, more of a footnote on the quest for life in our solar system, but Venus could not be completely ruled out as a host for life.

Continue Reading »

No responses yet

Sep 04 2020

Impossible Black Hole Collision Detected

Published by under Astronomy

Of course “impossible” is a relative term here. What is happening is that our knowledge of black holes is greatly expanding because we have a new tool for observing them – gravitational wave detectors. In fact, gravitational wave astronomy is a new science, and we are still on the very steep part of the learning curve.

But let’s back up and give some background. First – what’s a black hole? These are massive objects, mostly stellar remnants. At the end of a star’s life, when it has consumed all the fuel it is capable of fusing, the outward pressure from the fusion is gone and the inward force of gravity prevails. For small suns, like our own, they simply collapse down to a white dwarf, which has, for example, the mass of our sun but the size of the Earth. What keeps a white dwarf from collapsing even further is called degeneracy pressure. The simple (although not complete) explanation for this is the Pauli Exclusion Principle – particles cannot occupy the same state and location at the same time.

Larger stars with larger remnants collapse down even further, overcoming the degeneracy pressure and collapsing down to a neutron star. Again, the simplified version of this is that the electrons and protons merge to form neutrons, so the entire remnant is like one giant neutron. The mass limit for collapsing into a neutron star is about 1.44 solar masses. But also, stars big enough to leave behind a neutron star are also big enough to go supernova. This means the star itself has to be bigger than three solar masses, because much of the mass will be thrown off during the supernova and a smaller remnant will be left behind. Neutron stars are held up by neutron degeneracy pressure.

Even bigger stars that leave behind a stellar remnant of about 3 solar masses or larger, which means the star itself was about 20 solar masses or larger, result in a black hole. The neutron star of 3 M or greater overcomes even neutron degeneracy pressure – in fact, the gravitational force in this situation is greater than any other force we know of in the universe. Nothing can stop that remnant from continuing to collapse, all the way down to a single point in space – a singularity. That is a black hole.

Continue Reading »

No responses yet

Aug 25 2020

Supernova Mass Extinction

Published by under Astronomy

Over the history of life on Earth there have been many extinction events, but the top 5 mass extinctions are the big ones. Fortunately, such events don’t happen often. Understanding what caused these massive die-offs is inherently interesting, just so that we better understand the world, but might also provide some insight into potential future threats. A recent study suggests an interesting potential cause for one of these mass extinctions – nearby supernova.

These 5 mass extinction events are:

Ordovician-Silurian extinction – 444 million years ago – this is thought to have been caused by global cooling, resulting in increased polar ice, dropping of the ocean which reduced shallow habitats and changed its chemistry, allowing for more toxic minerals and less oxygen. This extinction saw the loss of 85% of species.

Late Devonian extinctions – 383-359 million years ago – this extinction correlates with a dramatic decrease in ocean oxygenation. The cause of this drop is not well understood, but candidates include asteroid impact, volcanic eruptions, and increased soil weathering due to the evolution of land plants. The species loss in this extinction was 70-80%.

Permian-Triassic extinction – 252 million years ago – this is the biggest mass extinction on Earth ever. Over 96% of sea species, and 75% of land species went extinct over about 60,000 years. Ecosystems did not recover for millions of years. These numbers actually underestimate the devastation, as these are the loss of species. But if you look at individual creatures, almost everything on Earth died, which just the slightest residue of life left. This was probably triggered by massive volcanic activity, releasing CO2, warming the planet, and causing acid rain.

Triassic-Jurassic extinction – 201 million years ago – this was caused also by global warming from an increase in atmospheric CO2 by a factor of four. This was in turn also caused by volcanic activity – this time from the Central Atlantic Magmatic Province. In this extinction about 80% of species were lost.

Cretaceous-Paleogene extinction – 66 million years ago – this is the one everyone knows about, because it saw the end of the non-avian dinosaurs. This was almost certainly caused by a large impact, but there persists a minority opinion regarding the contribution of volcanic activity from the Deccan Traps in what is now India. Along with the non-avian dinosaurs, 76% of species on Earth went extinct.

Continue Reading »

No responses yet

Aug 11 2020

Ceres an Ocean World

Published by under Astronomy

It seems we can add the dwarf planet, Ceres, to the list of ocean worlds in the solar system. These are planets or moons that have vast oceans beneath their surface – Earth is the only world with stable liquid water on its surface. These worlds are of particular interest because liquid water means the potential for life.

Ceres is the largest object in the asteroid belt between Mars and Jupiter. When it was first discovered it was categorized as a planet. Then it was discovered that it was the largest member of a belt of objects, and so it was “downgraded” to an asteroid (although the king of the asteroids). But then in 2006 the International Astronomical Union (IAU) famously created the new category of dwarf planet. Pluto was then demoted from full planet status to dwarf planet, but Ceres was upgraded also to a dwarf planet. These are worlds that orbit the sun, are not satellites, are large enough to pull themselves into a rough sphere, but have not cleared out their orbit of other large objects.

The recent study, based on data from the Dawn probe which did close up high-resolution imaging of Ceres (coming as close as 35 km) strongly suggests that there is at least a regional subsurface briny ocean on Ceres. The bright spot in Occator crater, which formed 22 million years ago from an impact, appears to be salt left behind by salty water leaking to the surface at the site of impact. The water then evaporated, leaving behind the highly reflective salt. This bright spot is a very unusual feature, that quickly grabbed attention when the Dawn probe images were first coming back.

At the very least, therefore, there is a large salty ocean beneath that crater. It is unknown if the ocean is regional or global, but even if regional it still qualifies Ceres as an ocean world.  It joins the list which includes the moons of Jupiter Europa, Ganymede, and Callisto, the moons of Saturn Enceladus and Titan, and possible (still unconfirmed) Saturn moon Mimas and the moon of Neptune, Triton. Astronomers believe that the subsurface ocean of Ceres must be slowly freezing. Moons of gas giants have tidal forces to produce internal heat and keep their oceans liquid.

Continue Reading »

No responses yet

Jul 07 2020

Mystery of the Disappearing Star

Published by under Astronomy

Stars do not just disappear – except when they do.

Using the Very Large Telescope (part of the European Southern Observatory) astronomers have been tracking a massive unstable star. The star is located in the Kinman Dwarf galaxy, which is a distant, small, and metal poor galaxy (PHL 293B – at a distance of 23.1 Mpc ). This is too far away for current telescopes to resolve individual stars, but astronomers can detect the presence of specific stars by looking at the spectral absorption lines. Between 2001 and 2011 they were monitoring a luminous blue variable star (LBV). These are massive blue stars, and this one was believed to be at the end of its life. They were able to infer temperature and other features that suggests the star was in an eruptive phase.

Then, in 2019, astronomers wanted to check back up on this star so they looked for the spectral lines in the same location of Kinman and – they were gone. The star was apparently gone. What could have happened?

The astronomers have put forth two hypotheses. The first is more mundane – if the star was in an eruptive phase, perhaps it shed a lot of its mass, rapidly becoming a much smaller and dimmer star (sometime between 2011 and 2019). This alone would not be enough to explain the disappearance, and so over this same time the star might also have been obscured by dust. This combination of factors could explain the disappearance.

Continue Reading »

No responses yet

Jun 25 2020

Mass Gap Object Discovered

Published by under Astronomy

Trust me, this is cool. Astronomers have discovered a stellar remnant with 2.6 solar masses, which is within a range of mass called the “mass gap” because of the almost complete lack of such objects in that range.  This is both an astronomy mystery (how do such objects form) and a physics mystery (what forces dominate at this size). Any new data points give us clues to solve the mystery of the mass gap, so this is exciting news.

Even still, yet again I find the headlines and even the popular reporting hyping the find. The BBC headline reads, “‘Black neutron star’ discovery changes astronomy.” No, this is not going to “change astronomy,” unless you count every incremental addition of new information as changing the entire field. Also, calling it a “black neutron star”, while a possibility, is assuming only one possible conclusion. But let’s get into the interesting details.

For quick background, when stars die they leave behind a stellar remnant. When stars run out of fuel they are able to burn (which is partly determined by their mass) they no longer produce the outward pressure of fusion and so gravity takes over and they collapse. If they are large enough (8-15 solar masses) the core collapse results in a supernova. Either way, what’s left behind is a stellar remnant. Small remnants become a white dwarf, a glowing hot ember but without fusion. If the remnant is at least 1.4 solar masses the force of gravity will overcome the repulsive force among the positive proton and negative electrons and the white dwarf will collapse down to a neutron star – in simplistic terms, the electrons and protons will merge into neutrons, so the entire thing is made of neutrons.

Continue Reading »

No responses yet

Jun 18 2020

Intelligent Life in the Galaxy

Published by under Astronomy

The headlines (taken from the press release) read: “New light shed on intelligent life existing across the galaxy.” But here’s the thing – I don’t think the referenced study does that at all. So what are they talking about?

The study uses their own version of the Drake Equation, which is a way of calculating how many spacefaring civilizations there are likely to be in the universe. The equation itself is correct – you consider the number of stars, the subset of those with planets in the habitable zone, the number of those who develop life, then intelligent life, then technology and multiply all that by the average lifespan of such civilizations. The equation works, as far as it goes, it’s just not terribly useful. The reason is that we don’t know the values of any of the variables. We can guess some of them, those dealing with stuff we can see, like how many planets are out there, but we essentially have no idea about any of the variables dealing with life.

The reason we have no idea is basic scientific logic – because we have one data point, Earth. Remember when we encountered the first interstellar object? That one encounter left us with no practical way to calculate how common such objects were. It could have been a one-off extremely unlikely event. But as soon as we encountered a second interstellar object, we had a rough idea how common they were. We had something to calculate.

You just can’t extrapolate from one data point. We may be the only life in the entire universe, or the universe might be teeming with life – both ends of the spectrum are consistent with our one known data point. We have no idea how common life is, how common intelligent life is, or technological civilizations, or how long they survive on average. None – really. So any numbers we put in are just wild guesses, and the errors on those wild guesses multiply.

Continue Reading »

No responses yet

Apr 21 2020

The Strange Interstellar Comet

Published by under Astronomy

Is our solar system similar to other solar systems? That’s actually a complex question with many layers. We know that there are different types of stars, varying mainly on their mass and age. We have a yellow sun, but a system around a red, orange, or blue sun is likely to be very different. We also know that at different relative locations in the galaxy the composition of the gas clouds out of which stellar systems form can be very different. One specific difference is known as “metallicity” – which refers to the amount of elements heavier than hydrogen or helium. Older stars were formed before a lot of heavier elements were made, so they have lower mellacity. This feature also varies within our galaxy, with higher metallicity closer to the center. And different galaxies have different mettalicity.

But what should we expect from a stellar system with a yellow sun at a similar location in our own galaxy? If the known variables are the same, should we expect the compositions of elements to also be roughly the same? This gets to the deeper scientific question of how typical our system is. Can we assume that the rest of the universe is similar to our tiny little corner of it? To counteract the hubris of humanity in thinking that we are somehow special, scientists try to follow the principle to assume that we are ordinary. But is that assumption always correct?

How can we even answer this question for stars that are light-years away? The primary method that we use is spectral analysis  (spectroscopy) – an awesomely powerful tool that allows us to identify specific elements and chemicals simply from analyzing the light we see from it. You can do a spectral analysis in a lab on a sample, or you can do it with telescopes on distant objects. The method is actually fairly simply. You use a prism to spread out the light into its color spectrum (like a rainbow). You can then analyze the emission lines or absorption lines which are like a signature.

Continue Reading »

No responses yet

Apr 20 2020

Crew Dragon Launches in May

Published by under Astronomy,Technology

Amid the current crisis there is some good news and significant progress – America is returning to crewed spaceflight after a 9 year gap. Scheduled for May 27th is the first crewed mission of the Space X Dragon capsule, which will send two astronauts to the ISS,  Bob Behnken and Doug Hurley. Technically this is the last test flight of the Crew Dragon capsule (the mission is called Demo-2). Last March the Demo-1 mission sent an uncrewed Dragon capsule to the ISS. The two astronauts will remain for an “extended” stay on the ISS, and then return in the capsule, splashing down in the Atlantic and recovered by a Space X recovery vessel.

If successful this will mark the return of America’s ability to send astronauts into orbit. It will also mark the first time a commercial company has done so, and is a significant milestone in the commercialization of space flight. The launch will be done in cooperation with NASA, lifting off from Pad 39A, which is the same one that launched Apollo and the Space Shuttle. The capsule will also be lifted to the ISS by a Falcon 9 rocket, which is also made by Space X. This is the rocket that can land again vertically and be reused.

There has been some back and forth on whether or not the Crew Dragon capsules themselves can be reused. Initially Musk predicted that the capsule could be reused many times, reducing the cost of getting astronauts into space. Then in 2018 they quietly backed away from this goal. The reason is that after a salt-water landing, it is time consuming (a year) and expensive to service the capsule for reuse. In order for capsule reuse to be practical you need a dry landing, which was the original plan of Space X. Apparently that has proven technologically difficult, so Space X is settling for salt-water landings, which means no reuse. However, the Crew Dragon capsule can more easily be refurbished and reused for Cargo Dragon missions without astronauts. Therefore, they will be used for this purpose. Space X has reused multiple Cargo Dragon capsules multiple time.

Continue Reading »

No responses yet

Mar 30 2020

Building Moon Bases Using Urine

Published by under Astronomy,Technology

This is an interesting idea that will probably not be actually implemented (although not impossible) but does raise some important points. A paper explores the viability of using urea from human urine as an agent in lunar concrete. Why is something like this even being considered?

The overwhelmingly dominant factor of building anything on the Moon is that it costs about $10,000 to put one pound of anything into Earth orbit, and more to take it to the Moon (although most of the energy would be used just getting into orbit). This is why it is a high priority for NASA to reduce the cost of getting stuff into space. Elon Musk has also made this a priority and SpaceX is geared mainly toward this purpose. Even if they reach their goal of reducing the cost by 10 fold, to about $1000 per pound, that still adds up when you are trying to build an entire Moon base. One solution is to use as much native material as possible.

Let’s talk a bit about the lunar regolith. The term regolith just refers to any loose material on top of the rocks on a world’s surface. The Earth has regolith, we call it dirt, sand, or soil. The lunar regolith is the result of micrometeors pulverizing the lunar surface for billions of years. In most locations the regolith extends down 4-5 meters, but can be as deep as 15 meters in places. Because of the absence of natural erosion from wind, water, or biological activity, the lunar regolith remains sharp and pointy. So the Moon is basically covered with a deep blanket of fine but jagged dust.

Continue Reading »

No responses yet

Next »