We think of habitable exoplanets as residing in a star’s habitable zone. That makes sense, right? It’s the region around a star where liquid water might exist, perhaps on a rocky planet similar to Earth. But there might be another important zone – related to habitability – that astronomers have mostly overlooked: the soot zone. Researchers at the University of Michigan said on May 25, 2023, that astronomers could expand the search for habitable exoplanets by taking the soot zone into account.

This zone in a protoplanetary disk – or planet-forming – is the space between the star and the soot line.

The researchers published their peer-reviewed findings in The Astrophysical Journal Letters on May 25, 2023.

Expanding the search for habitable exoplanets

The habitable zone is typically the first place that astronomers look for potentially habitable planets. That is based on what we know about our own solar system, and how the Earth has been able to hold onto its oceans and other water. Earth resides within the sun’s habitable zone while Mars and Venus are near the outskirts.

But astronomer Ted Bergin, who led the study, and his colleagues want to also consider the soot zone. The soot zone is the space between the star and the soot line. The soot line, specifically, is the outer boundary near a star where solid carbon molecules are destroyed and sublimate into gas. They become volatile carbon compounds instead of remaining as solid ones. Volatiles are chemical elements and compounds that can vaporize easily.

Planets in this zone may be rich in volatile carbon compounds, and those compounds could be quite different than anything on our own planet. What would such planets be like? Could they be habitable?

Bergin said:

It adds a new dimension in our search for habitability. It may be a negative dimension or it may be a positive dimension. It’s exciting because it leads to all kinds of endless possibilities.

Water-poor and carbon-poor Earth

But these planets may also be water-poor. That sounds bad for habitability, but Earth is water-poor as well. Surprisingly, our planet contains only 0.1% water by mass.

Because of such little water content, scientists have long thought that Earth formed inside the frost line, or water-ice line, which is farther out from the sun. Bodies beyond that line tend to have a greater amount of water, percentage-wise, like the icy moons with subsurface oceans.

We also think of Earth as carbon-rich, but, as with water, it’s carbon-poor. Scientists say that while our planet was forming, it received only about one carbon atom per 100 that were available in the protoplanetary disk. The soot line may be responsible for this. If the building blocks of the young Earth formed inside the soot line, closer to the sun, then the volatile carbon compounds would have been turned into gas. That would limit the amount of solid carbon available for the forming planet.

Planets between the soot line and frost line

The study also focuses on exoplanets born between the soot line and frost line. There aren’t any in our own solar system, but astronomers have discovered many in other solar systems. They are typically super-Earth and mini-Neptune worlds. Both are larger in mass than Earth, but smaller in mass than Neptune. They are also the most common type of exoplanets found so far. Bergin said:

These are either big rocks or small gas giants; that’s the most common type of planetary system. So maybe, within all those other solar systems out in the Milky Way galaxy, there exists a population of bodies that we haven’t recognized before that have much more carbon in their interiors. What are the consequences of that? What this means for habitability should be explored.

Hazy methane atmospheres

The researchers modeled what these planets would be like, and found that they would likely have very hazy atmospheres. In the study, these planets, in the soot zone, are silicate-rich, with between 0.1% and 1% carbon by mass. They also have variable amounts of water. The models suggested that these worlds would outgass volatile carbon compounds and develop methane-rich atmospheres. The methane atmosphere would produce hazes, due to interaction with photons from the planets’ host stars. This is similar to how the hydrocarbon haze in Titan’s atmosphere is produced. Bergin explained:

Planets that are born within this region, which exists in every planet-forming disk system, will release more volatile carbon from their mantles. This could readily lead to the natural production of hazes. Such hazes have been observed in the atmospheres of exoplanets and have the potential to change the calculus for what we consider habitable worlds.

So, are those exoplanets habitable?

This could mean that a planet like this is potentially habitable, since the haze is evidence for a possibly carbon-rich mantle on the planet. And life – as we know it on Earth – is based on carbon. But with potentially more carbon and methane-rich atmospheres, these worlds would be quite unlike Earth in many ways.

Bergin added:

If this is true, then there could be a common class of haze planets with abundant volatile carbon, and what that means for habitability needs to be explored. But then there’s the other aspect: What if you have an Earth-sized world, where you have more carbon than Earth has? What does that mean for habitability, for life? We don’t know, and that’s exciting.

NASA’s James Webb Space Telescope (JWST) will be able to look at some of these worlds, as the paper notes:

Such hazes, and the methane that drives their formation, are detectable via JWST transit spectroscopy, as demonstrated here, especially around stars lower in mass (and therefore size) than the sun.

That, too, will be exciting.

Bottom line: Astronomers say that habitable exoplanets could form in the soot zone around young stars. They could be rich in volatile carbon compounds, different from Earth.

Source: Exoplanet Volatile Carbon Content as a Natural Pathway for Haze Formation

Via University of Michigan

Saturn’s moon Enceladus is famous for its huge, active plumes of water vapor. They erupt like geysers at this little moon’s south pole. NASA’s Cassini spacecraft discovered them in 2005. And scientists quickly surmised that the plumes originate from a global ocean below the surface of Saturn’s moon. That subsurface ocean might be inhabited by living things. So the plumes might contain evidence of life. In May 2023, we began to hear that the James Webb Space Telescope (JWST) has now taken a new close look at Enceladus. Webb has observed a new, much larger plume.

The water vapor plumes on Enceladus can be huge, generally speaking. They tower above the moon’s icy surface. Consider that Enceladus itself is only about 314 miles (505 km) wide. The plumes spotted by Cassini were known to be at least as tall as the moon’s diameter. But this new plume – observed by Webb – is the biggest one ever seen, many times the diameter of Enceladus itself. As Sara Faggi, a planetary astronomer at NASA’s Goddard Space Flight Center, said:

It’s immense.

Biggest water plume on Enceladus ever seen

We haven’t seen a statement from scientists about the new plume. And we haven’t seen the Webb image. It apparently hasn’t been released yet.

But Alexandra Witze wrote about the new plume in Nature on May 18, 2023.

And Faggi mentioned the plume and the Webb observations at a conference at the Space Telescope Science Institute in Baltimore, Maryland, on May 17.

While few details were presented at the conference, Faggi said that a new paper will be coming out soon.

Many times Enceladus’ diameter

The water vapor erupts through large cracks in Enceladus’ icy surface. Scientists call these cracks tiger stripes.

The venting was known for sending the water vapor and other particles it contains a long way from Enceladus, out into space. But this newest eruption sent spray from the moon’s interior even farther out, up to many times Enceladus’ diameter of 314 miles (505 km).

Webb was able to observe this plume on November 22, 2022, and scientists have been studying the data sent back ever since.

Cassini analyzed particles in the plume that were relatively close to Enceladus itself. But Webb has the advantage of being able to look at plume particles that travel much farther away from the little moon. The ability to study both will help scientists better understand the plumes and the rich variety of ingredients they contain.

New analysis of Enceladus’ plumes

The analysis of the plume material, to be presented in the forthcoming paper, should be quite interesting. Cassini previously found that the plumes contain water vapor, ice particles, salts, silica, carbon dioxide, ammonia, methane and organic molecules.

Webb observed the plume for only 4.5 minutes, but that was ample time to obtain the data needed. The analysis will provide more details about how much water vapor the plume contained and the temperature. This plume, however, since it is so spread out away from Enceladus, is likely much more diffuse than the plumes Cassini saw (and actually flew through!). That may make it more difficult to determine what kinds of organic molecules were in the plume. Cassini did find a variety of both simple and complex organic molecules during its mission, however. As Witze wrote:

But the plume is likely to be of low density, more like a diffuse, cold cloud than a damp spray. That’s not great news for anyone looking to grab samples from the plume and hoping to find life, because the signs of life might be too sparse to detect. Ice grains seen by Cassini much closer to Enceladus are more likely to have high concentrations of organic particles, says Shannon MacKenzie, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

With that in mind, Webb did find an abundance of intriguing chemicals in the plume. Witze wrote:

JWST also analyzed the spectrum of sunlight reflecting off Enceladus and found evidence of many chemicals, including water and possibly other compounds that could hint at geological or biological activity in the moon’s ocean.

What are they? We’ll have to wait to find out, but as Faggi noted:

We have many more surprises.

Life on Enceladus?

The plumes are of special interest to science because they might contain clues about possible life in Enceladus’ subsurface ocean. The ingredients found so far are tantalizing, although not proof yet that the ocean harbors living organisms.

Cassini did also find evidence suggesting that there are hydrothermal vents on the ocean floor. If so, they could possibly be a source of heat and nutrients, just as they are in oceans on Earth.

Future missions

As of now, there are no confirmed missions going back to Enceladus. But there are ideas on the drawing boards, such as a combination of orbiter and lander called Orbilander. Read the concept study here. A return mission will be essential to find out whether life ever has existed on Enceladus, or still does.

Bottom line: NASA’s Webb Space Telescope has observed the largest water plume on Enceladus ever seen. Details about the analysis results will be published in a new paper.

Via Nature

New Pillars of Creation and more

On May 23, 2023, NASA released four new composite images from the Chandra X-ray Observatory and the James Webb Space Telescope. The newly combined images include two galaxies, a nebula (the famous Pillars of Creation) and a star cluster. Chandra studies objects in X-ray and captures objects in the high-energy range of the electromagnetic spectrum. Webb studies object in infrared light or objects in the low-energy range of the electromagnetic spectrum.

In addition to Chandra and Webb, the newly combined images use data from a few other sources. Astronomers used visible light data from the Hubble Space Telescope and the European Southern Observatory’s New Technology Telescope. Plus, they included infrared data from the Spitzer Space Telescope, as well as X-ray data from ESA’s XMM-Newton scope. By the way, neither X-ray nor infrared light is visible to our unaided eyes.

Chandra-Webb composite of a nebula and star cluster

The Pillars of Creation is a stunning area of the sky made famous by the Hubble Space Telescope. Also, it’s part of the Eagle Nebula, aka Messier 16. The Webb portion of the new image reveals the columns of gas and dust (in red, green and blue) surrounding some recently formed stars. Then the Chandra portion reveals the strong X-ray emissions (in red and blue) coming from the young, hot stars.

Next up is the star cluster NGC 346 in one of our neighboring galaxies, the Small Magellanic Cloud (SMC). The SMC is located 200,000 light-years away. The plumes and arcs are gas and dust where stars and planets can form and are from Webb images. The purple cloud is the result of a massive star exploding as a supernova and is from Chandra images. The Chandra data also include powerful stellar winds blowing off hot and massive young stars. Note: X-ray data are purple and blue, and the infrared and optical data are red, green and blue.

And the galaxy images

And then there is the barred spiral galaxy NGC 1672. The combined image used Chandra (and other X-ray data) to indicate remains of energetic objects like neutron stars and black holes sucking in material from stars close enough to be caught by their gravity. Then the optical and infrared portion of the image – including data from both the Hubble and Chandra – shows the gas and dust of the galaxy’s spiral arms. Note: X-ray data are purple, the optical and infrared data are red, green and blue.

Finally is the face-on spiral galaxy Messier 74. It’s also called the Phantom Galaxy due to a low-surface brightness making it difficult to spot in small telescopes. It’s one of the hardest objects to catch during a Messier Marathon. So the infrared portion from the Webb telescope reveals the gas and dust, while the X-ray data from Chandra bring out the high-energy stars. Then, the optical data from the Hubble show less energetic stars and dust lanes. Note: X-ray data are purple, optical data are orange, cyan and blue, and infrared data are green, yellow, red and magenta.

Bottom line: NASA combined images from the Chandra X-Ray Observatory and the Webb Space Telescope – plus other telescopes – and shared this video of the newly released images.

Via NASA

Comets are rare in the asteroid belt between the planets Mars and Jupiter. But some comets do reside there, including Comet Read (238P/Read). Asteroids tend to be rocky or metallic. Unlike them, Comet Read – an icy body – sometimes looks fuzzy, displaying, like other comets, a coma and a tail. On May 15, 2023, NASA said the Webb space telescope has taken a close look at Comet Read. Webb confirmed water vapor, a first for a comet in the asteroid belt. More unexpected was what Webb didn’t find. It found no sign of carbon dioxide, a gas expected and observed in most comets.

A team of scientists in the U.S. published the peer-reviewed results on May 15, 2023, in Nature.

Weird comet 238P/Read

Comets are typically rich in water vapor and water ice, as well as gas and dust. Scientists think they may even have brought much of Earth’s original water to our planet billions of years ago. But when it comes to the rarer comets in the main asteroid belt, proof of water vapor or ice has been hard to come by … until now.

For the first time, water vapor has been definitively detected on a comet – Comet Read – in the main asteroid belt. Lead author Michael Kelley of the University of Maryland said:

In the past, we’ve seen objects in the main belt with all the characteristics of comets, but only with this precise spectral data from Webb can we say yes, it’s definitely water ice that is creating that effect. With Webb’s observations of Comet Read, we can now demonstrate that water ice from the early solar system can be preserved in the asteroid belt.

Missing carbon dioxide

There was, however, another result that surprised scientists. Webb found no carbon dioxide (CO₂) on the comet. The paper stated:

Here, we present JWST [James Webb Space Telescope] observations which clearly show that main-belt comet 238P/Read has a coma of water vapor, but lacks a significant CO₂ gas coma.

Carbon dioxide tends to compose about 10% of the volatile material in comets. So why is it missing in Comet Read?

The researchers pose two possible scenarios to explain the missing carbon dioxide. The first possibility is that the comet did have it a long time ago but ended up losing it because of the warmer temperatures in the asteroid belt. (Comets generally reside and originate in the Kuiper Belt and Oort Cloud, out past Neptune). As Kelley explained:

Being in the asteroid belt for a long time could do it; carbon dioxide vaporizes more easily than water ice, and could percolate out over billions of years.

The other theory is that Comet Read originated in a warmer region of the solar system where there was no carbon dioxide to begin with.

Additional observations and maybe even a mission?

The results are interesting, but do they represent asteroid-belt comets in general, or is Comet Read simply unusual? To find out, astronomers will now use Webb to look at other comets in that part of the solar system as well. This will be part of Webb’s Guaranteed Time Observations. Co-author Heidi Hammel is with the Association of Universities for Research in Astronomy (AURA). She said:

These objects in the asteroid belt are small and faint, and with Webb we can finally see what is going on with them and draw some conclusions. Do other main-belt comets also lack carbon dioxide? Either way it will be exciting to find out.

There is even the possibility of sending a robotic spacecraft mission out to one of these comets. Co-author Stefanie Milam, Webb deputy project scientist for planetary science, surmised:

Now that Webb has confirmed there is water preserved as close as the asteroid belt, it would be fascinating to follow up on this discovery with a sample-collection mission and learn what else the main belt comets can tell us.

The findings show how comets aren’t all alike as much as we might tend to think. The differences, and similarities, between comets in various parts of the solar system can provide valuable clues as to how they – and the solar system overall – first formed. And maybe even how life first originated on Earth, and perhaps elsewhere in our sun’s family of worlds.

Bottom line: The Webb telescope has observed Comet Read, a weird comet in the main asteroid belt. Among the findings … water vapor, yes. But carbon dioxide, no.

Source: Spectroscopic identification of water emission from a main-belt comet

Via Webb Space Telescope

[youtube https://www.youtube.com/watch?v=VF5nQyBwSlI&w=800&h=450]
Watch this video to learn more about NASA’s summer 2023 Astrophoto Challenge.

NASA’s Astrophoto Challenge

NASA is holding an Astrophoto Challenge for summer 2023, which runs from May 15 to July 31. The focus of this summer’s challenge is the dramatic Phantom Galaxy, M74. You can use real astronomical data and tools to create your own images and explore the mysterious structures within this galaxy. Or, just create an image that you think is beautiful.

In the challenge, you have the opportunity to capture your own real-time telescope image using the MicroObservatory robotic telescope network. You can also work with an archival set of data files taken with multi-wavelength NASA, ESA, and CSA space telescope missions (Webb, Hubble, Chandra, Spitzer, and XMM-Newton).

NASA’s Astrophoto Challenge includes instructions on how to turn the data into beautiful composite images with a simple and free web-based image processing tool used by professional astronomers. The JS9 image processing tool is widely used by the astronomical community to process and analyze the data. NASA’s Astrophoto Challenge uses a version of this tool, JS9-4L, developed for learners.

What is the Phantom Galaxy?

The Phantom Galaxy – M74 – lies in the constellation Pisces. The galaxy is home to about 100 billion stars. It was the focus of one of the Webb Space Telescope’s earliest images. Scientists have spotted three supernovas in the galaxy, in 2002, 2003 and 2013. The galaxy may also be home to an uncommonly sized intermediate-mass black hole.

Follow this link to join the summer 2023 Astrophoto Challenge.

Bottom line: NASA invites the public to participate in its Astrophoto Challenge for summer 2023. Learn the details here.

Early-universe prequel: Galaxies in distant space

We know our universe contains gigantic galaxy clusters in space. Each galaxy is made of millions to billions of stars. And each cluster is made of hundreds to thousands of galaxies, bound together by gravity. And the clusters group into even-larger superclusters, with vast voids in between. Now consider that looking far away in space is the same as looking back in time. That’s why we can use the most powerful of modern telescopes to peer into the early universe, and see an early-universe prequel – a precursor, a forerunner – to one of the huge galaxy clusters we see today.

In other words, what you see above is an image – from the new Webb Space Telescope, which launched in late 2021 and was placed at the L2 point in the Earth-sun system – of seven exceedingly distant galaxies. They are young galaxies in the early universe, confirmed at a distance that astronomers refer to as redshift 7.9. That distance away in space correlates to 650 million years after the Big Bang, the event that gave rise to our universe 13.8 billion years ago. The European Space Agency said in late April:

This makes them the earliest galaxies yet to be spectroscopically confirmed as part of a developing cluster.

These results have been published in The Astrophysical Journal Letters.

How astronomers noticed these galaxies

Webb wasn’t the first space telescope to see these galaxies. The Hubble Space Telescope’s Frontier Fields program – which ran from 2013 to 2017 – also spotted them. It was Frontier Fields that first established the galaxies as candidates for further observation. ESA said:

Frontier Fields dedicated Hubble time to observations using gravitational lensing, to observe very distant galaxies in detail. However, because Hubble cannot detect light beyond near-infrared, there is only so much detail it can see. Webb picked up the investigation, focusing on the galaxies scouted by Hubble and gathering detailed spectroscopic data in addition to imagery.

See a Wikipedia entry containing a list of deep fields, in part from Frontier Fields

What Webb brings to the table

The James Webb Space Telescope is an international collaboration among NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). ESA said:

Astronomers used Webb’s Near-Infrared Spectrograph (NIRSpec) instrument to precisely measure the distances and determine that the galaxies are part of a developing cluster. Galaxy YD4, previously estimated to be at a further distance based on imaging data alone, was able to be more accurately placed at the same redshift as the other galaxies.

Before Webb, astronomers did not have high resolution imaging or spectral infrared data available to do this type of science.

At extreme distances, astronomers use the redshift reference to account for the fact that, as the universe expands, wavelengths of light are stretched and ‘shifted’ to redder wavelengths, which are longer. Shorter wavelengths, for example ultraviolet and X-ray, are toward the bluer end of the electromagnetic spectrum. So extreme distances in the early universe are referenced by how much the light emitted there has been shifted as it travelled through space to be detected by a telescope.

Bottom line: We know our universe consists of gigantic galaxy clusters in space. And we know that looking far away in space equals looking back in time. Here’s an early-universe prequel to a huge galaxy cluster.

Via ESA

Do galaxy collisions power quasars?

Astronomers at the University of Sheffield in the UK said this morning (April 26, 2023) they have new observations in hand, proving that colliding galaxies power quasars.

Quasars are the most powerful objects in the universe. They’re thought to shine as brightly as a trillion stars, yet are packed into a space as small as our solar system. And what could generate so much energy in so small a space? The most popular models feature galaxies in the process of formation, and supermassive black holes at the quasars’ hearts.

The new work suggests colliding galaxies as the cause of quasars’ magnificent power. And it suggests that our home galaxy – the Milky Way – will become a quasar when it collides with the nearby Andromeda galaxy, billions of years from now.

New observations of 48 galaxies

The Sheffield astronomers said they used deep imaging observations from the Isaac Newton Telescope in La Palma, an island in the Canary Islands. They observed 48 galaxies that host quasars – and compared them to 100 galaxies without quasars – to learn that galaxy collisions ignite the quasars. They observed:

… the presence of distorted structures in the outer regions of the galaxies that are home to quasars.

And they explained:

When two galaxies collide, gravitational forces push huge amounts of gas towards supermassive black holes at the center of the remnant galaxy system that results from the collision … just before the gas is consumed by the black hole, it releases extraordinary amounts of energy in the form of radiation, resulting in a quasar.

Adding:

The Milky Way is likely to experience its own quasar when it collides with the Andromeda galaxy in roughly five billion years’ time.

Here’s how it works

The astronomers’ statement explained:

Most galaxies have supermassive black holes at their centers. They also contain substantial amounts of gas. But most of the time this gas is orbiting at large distances from the galaxy centers, out of reach of the black holes.

Collisions between galaxies drive the gas towards the black hole at the galaxy centre; just before the gas is consumed by the black hole, it releases extraordinary amounts of energy in the form of radiation, resulting in the characteristic quasar brilliance.

The ignition of a quasar can have dramatic consequences for entire galaxies. It can drive the rest of the gas out of the galaxy, which prevents it from forming new stars for billions of years into the future.

This is the first time that a sample of quasars of this size has been imaged with this level of sensitivity …

And that additional sensitivity must be what’s creating confidence in these researchers that they’ve “solved” the mystery of quasars. Their statement said:

By comparing observations of 48 quasars and their host galaxies with images of over 100 non-quasar galaxies, researchers concluded that galaxies hosting quasars are approximately three times as likely to be interacting or colliding with other galaxies.

The study has provided a significant step forward in our understanding of how these powerful objects are triggered and fuelled.

The Sheffield astronomers are excited

Astrophysicist Clive Tadhunter of the University of Sheffield said:

Quasars are one of the most extreme phenomena in the universe. And what we see is likely to represent the future of our own Milky Way galaxy when it collides with the Andromeda galaxy in about five billion years.

It’s exciting to observe these events and finally understand why they occur. But thankfully Earth won’t be anywhere near one of these apocalyptic episodes for quite some time.

The researchers also pointed out that quasars are important to astrophysicists because, due to their brightness, they stand out at large distances and therefore act as “beacons” to the earliest epochs in the history of the universe. Jonny Pierce at the University of Hertfordshire explained:

It’s an area that scientists around the world are keen to learn more about. One of the main scientific motivations for NASA’s James Webb Space Telescope was to study the earliest galaxies in the universe. And Webb is capable of detecting light from even the most distant quasars, emitted nearly 13 billion years ago.

Quasars play a key role in our understanding of the history of the universe … and possibly also the future of the Milky Way.

Bottom line: Do galaxy collisions power quasars? UK astronomers have evidence suggesting they do. If so, then our own Milky Way galaxy might someday become a quasar.

Via University of Sheffield