Archive for the 'Astronomy' Category

Nov 02 2020

Earth-Sized Rogue Planet Discovered

Published by under Astronomy

I like to keep my mental model of the universe updated as much as possible. One of the things I learned not too long ago about the universe is the frequency of “rogue” planets. These are planets that are not bound to any star. The dominant current theory is that most of these rogue planets formed in stellar discs just like bound planets but then at some point in their history interacted with another large body and were flung out of their stellar system. In fact, most planets that form in a stellar system may have unstable orbits that will doom them over the cosmological short term to either collide with another body, fall into their parent star, or get flung out of the system. Only those planets with stable orbits remain, and so eventually systems will settle down with a relatively few planets in stable orbits.

How many rogue planets (also called FFPs for free floating planet) are there in the Milky Way? We don’t know, and estimates vary wildly. The most cited recent estimate based upon computer simulations suggest that there are at least 50 billion rogue planets in the Milky Way. This is not much, actually, as there are between 100 and 400 billion stars, so that’s less than on per star. Still, that is a lot of rogue planets wandering the vast darkness of interstellar space. But other estimates of the number of rogue planets are much higher. At the high end one estimate put the number at 100,000 times greater than the number of stars. That seems implausible. But it suggests the number could be much higher than 50 billion. Even if on average there are several rogue planets for each stellar system, that would create hundreds of billions of such planets in our galaxy. And we have to include all the dead stars whose planets are still roaming interstellar space.

As an aside, any such estimate has to include a size parameter – how many FFPs of size greater than or equal to X. The estimates above use Pluto as the lower end of the size range. The lower you go, however, the greater the number.

What we need is some observational data to supplement the theoretical simulations. If we can do a survey looking for rogue planets then the number of such worlds we find can be plugged into our simulations to come up with better estimates for the total number. But how, you may be wondering (if you don’t know already) can we find a cold dark planet at the vast distances of interstellar space? Right now we find exoplanets by using a few methods. One method is the transit methods – we look at the dip in light output from a star as a planet passes in front of it. Another is the wobble method – we look for the wobble in the path of a star that indicates it is being tugged by a large planet going around it in its orbit. We might also be able to directly image a planet by looking at the reflected light off of it and removing the glare from the parent star. None of these methods will work for a rogue planet.

Continue Reading »

No responses yet

Oct 27 2020

Water on the Moon

Published by under Astronomy

A new paper published in Nature Astronomy presents further evidence for significant water near the surface of the Moon. This is exciting news for the prospects of a lunar base, especially since NASA is planning on returning permanently to the Moon by 20204.

The Artemis program (Artemis is the twin sister of Apollo) plans to put the first woman and the next man on the lunar surface by 2024. Even if they don’t meet this ambitious timeframe, they will likely succeed sometime this decade. Unlike the “flags and footprint” mission design of Apollo, Artemis is designed for sustained exploration of the Moon. Artemis will use the space launch system, which will be the most powerful rocket in the world. In fact, the most powerful configuration of the SLS will be more powerful than the Saturn V rocket. This is because the SLS was designed no only to return to the Moon, but to be powerful enough to get to Mars, which is the ultimate goal.

On top of the SLS will be the Orion capsule, NASA’s deep space capsule. Orion can accommodate up to four astronauts, and is designed for multi-week missions. It will have exercise equipment, radiation shielding, and on board waste disposal. When they get to the Moon they will have a new lunar lander, currently in development. But unlike Apollo, NASA also plans on building the Gateway – a lunar orbiting platform for long term occupation and exploration of the Moon.

After the initial Artemis missions, NASA plans to create a basecamp near the south-pole of the Moon for long term occupation and exploration of the Moon. Why the south pole? In NASA-speak the poles, “may contain mission-enhancing volatiles.”  In addition “These sites may also offer long-duration access to sunlight, direct-to-Earth communication, surface slope and roughness that will be less challenging for landers and astronauts.”

Continue Reading »

No responses yet

Oct 05 2020

Superhabitable Planets

Published by under Astronomy

Earth is so far the only planet in the universe which we know contains life. There are many other worlds in our own solar system that may contain life (or did at one time), but none confirmed. Part of the goal of the exoplanet exploration program is to determine how many worlds out there are capable of supporting life. This requires that we come up with some specific definition of a habitable world, and it is only natural that we will model that definition after our one data point – the Earth. But perhaps Earth is not the pinnacle of habitability.

Astrobiologists and exoplanet hunters have been considering this question for a while. A recent paper is the latest in the dialogue about what makes a planet habitable. Earth, of course, is perfect for Earth life, but it may not be the most habitable for life in general. By habitable astrobiologists mean that the world can not only contain life, but contain an abundance of life over a long period of time. So the authors of the recent paper set out to define optimal “superhabitability” and then find worlds in the exoplanet database that would best fit this definition.

I have to point out that still they were using Earth life as their standard. They are not considering, for example, hydrogen breathers or other exotic forms of life that would require entirely different environments. They are still building on the concept that life requires liquid water, and so the number one criterion is still a planet in the “Goldilocks” zone of its parent star that would allow for liquid water on the surface. The most superhabitable worlds, they argue, would be slightly larger than Earth, to maximize surface area for both oceans and land mass without having too much gravity. A larger world would also help the planet hold onto a sufficiently thick atmosphere for a long time.

A large planet has another potential advantage – it would remain geologically active for longer. The planet itself needs to retain some interior heat, which will only last for billions of years if there is radioactive material that will warm the planet as it decays. The Earth would have cooled long ago, for example, were it not for uranium, thorium, and other radioactive materials shedding heat at they decay. In any case, larger rocky worlds would cool more slowly.

Continue Reading »

No responses yet

Oct 02 2020

Speaking of Venus

Published by under Astronomy

I recently discussed the exciting news of the discovery of phosphine gas in the clouds of Venus. This is exciting because phosphine is a potential marker of life. It should not exist on a small rocky world, and there is no known abiotic source on Venus. Microbes in the clouds above Venus are a plausible source, although scientists are careful to point out this is not proof of life, just a possibility. This finding has renewed interest in exploring our nearest neighbor, and even prior to this discovery NASA was planning another probe to Venus. This probe will likely have its mission altered to follow up on the phosphine discovery.

Venus is also interesting because it likely had a complex history over the last several billion years. A recent computer simulation, in fact, indicates that it may have been hospitable to life on the surface more than a billion years ago. Now the surface of Venus is hot enough to melt lead, making it the hottest planet in the solar system – even hotter than Mercury, which is closer. This is due to the extreme greenhouse effect from its mostly carbon dioxide atmosphere. The clouds above Venus are largely sulphuric acid. But a billion years ago it may have been more similar to Earth.

The dramatic change in Venus, in turn, may be tied to Jupiter. This is further connected to what we are learning about how stellar systems typically evolve, by observing exoplanetary systems. We now have many more data points than just our own solar system. We have confirmed over 4,000 exoplanets to date, with thousands more detected and awaiting confirmation. We can usually tell the mass, volume, and distance from the parent star, and so can construct a basic diagram of each system. However, depending on the method of detection used, we do not typically find every planet in an exosystem. Methods are generally biased towards larger and closer worlds.

One of the things we have discovered is that some planets are so-called hot Jupiters – they are gas giants orbiting very close to their star. About 10% of expolanets are hot Jupiters, and about 1% of systems have at least one hot Jupiter. Again – our detection systems more easily discover large and close planets, so these ratios may not represent reality and may be an overestimation. But a the very least, hot Jupiters are common throughout the galaxy.

Continue Reading »

No responses yet

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

Next »