More Weird and Wild Planets

A world called TOI-849b could be the exposed, naked core of a former gas giant planet whose atmosphere was blasted away by its star.  Every day is a bad day on planet TOI-849b. . It hugs its star so tightly that a year – one trip around the star – takes less than a day. And it pays a high price for this close embrace: an estimated surface temperature of nearly 2,800 degrees Fahrenheit (1,500 degrees Celsius) It’s a scorcher even compared to Venus, which is 880 degrees Fahrenheit (471 degrees Celsius). About half the mass of our own Saturn, this planet orbits a Sun-like star more than 700 light-years from Earth. (NASA/Exoplanet Exploration Program)

The more we learn about the billions upon billions of planets that orbit beyond our solar system, the more we are surprised by the wild menagerie of objects out there.  From the start, many of these untolled planets have been startling, paradigm-breaking,  mysterious, hellish, potentially habitable and just plain weird.  Despite the confirmed detection of more than 4,000 exoplanets, the job of finding and characterizing these worlds remains in its early phases.  You could make the argument that  learning a lot more about these distant exoplanets and their solar systems is not just one of the great tasks of future astronomy, but of future science.

And that is why Many Worlds is returning to the subject of “Weird Planets,” which first appeared in this column at the opening of 2019.  It has been the most viewed column in our archive, and a day seldom goes by without someone — or some many people — decide to read it.

So here is not a really a sequel, but rather a continuation of writing about this unendingly rich subject.  And as I will describe further on,  almost all of the planets on display so far have been detected and characterized without ever having been seen.  The characteristics and colors presented in these (mostly) artistic renderings are the result of indirect observing and discovery — measuring how much light dims when a faraway planet crosses its host star, or how much the planet’s gravity causes its sun to move.

As a result, these planets are sometimes called “small, black shadows.” Scientists can infer a lot from the indirect measurements they make and from the beginnings of the grand effort to spectroscopically read the chemical makeup of exoplanet atmospheres. … Read more

Sparkling Gifts From the Hubble Space Telescope, Thirty Years Into Its Mission

This Hubble image captures globular star cluster (NGC 6541) that is roughly 22,000 light-years from Earth.  A globular cluster is a spherical collection of stars that orbits a galactic core. They are very tightly bound by gravity, which gives them their spherical shapes,and relatively high density of stars toward their centers.  The cluster is bright enough that backyard stargazers in the Southern Hemisphere can spot it with binoculars, though certainly not in this detail. (NASA, ESA, and G. Piotto (Università degli Studi di Padova)

For almost 30 years now, the Hubble Space Telescope has transformed how we see the cosmos.  In terms of scientific output as well as making visible the splendors of the sky above us, the Hubble has been arguably the most consequential telescope ever to peer into space.

To commemorate 30 years of Hubble science and images, NASA and the European Space Agency have released 30 previously unpublished images of galaxies, star clusters and nebula from what is known as the Caldwell catalogue,  a collection compiled by British amateur astronomer and science communicator Sir Patrick Caldwell-Moore.

These images have been taken by Hubble throughout its time in space and used for scientific research or for engineering tests, but NASA had not fully processed the images for public release until now.

At the end of a difficult year, they offer the glitter, the grandeur and the cosmic marvel  that the Hubble provides so well and that perhaps people could use right now.

This Hubble image captures a small region on the edge of the inky Coalsack Nebula.  A nebula is an enormous cloud of dust and gas occupying the space between stars and acting as a nursery for new stars.  Coalsack is a “dark nebula” which completely blocks out visible wavelengths of light from objects behind it. The image was made  using Hubble’s Advanced Camera for Surveys in both visible and infrared wavelengths.  (NASA, ESA, and R. Sahai of NASA’s Jet Propulsion Laboratory)

The Hubble famously entered into Earth orbit and began its mission with the calamitous discovery of a near-fatal mistake — the main mirror had been ground incorrectly and could not accomplish much viewing.  The telescope was about 340 miles from Earth and never before had NASA undertaken a mission to repair a spacecraft that far away.

But in 1993 seven astronauts flew to the Hubble on the space shuttle Endeavour, spent five days repairing it and the rest is history. … Read more

Japan’s Hayabusa2 Mission Returns to Earth

Fireball created by the Hayabusa2 re-entry capsule as it passes through the Earth’s atmosphere towards the ground (JAXA).

In the mission control room in Japan, all eyes were fixed on one of the large screens that ran along the far wall. The display showed the night sky, with stars twinkling in the blackness. We were waiting for a delivery from space.

Japan’s Hayabusa2 mission launched from the Tanegashima Space Center on December 3, 2014. The spacecraft was headed to asteroid Ryugu, with the intention of studying the tiny world and collecting a sample to return to Earth.

The mission would prove to be an incredible success. Not only did the spacecraft gather two samples from the asteroid, but it was the first mission to deploy autonomous rovers to explore an asteroid’s surface, generate an artificial crater in order to study the asteroid’s structure and collect a sample of the interior, and additionally, deploy a lander to make scientific measurements from the surface itself. The mission finale was to return the samples safely back to Earth on December 6, 2020. The grains in that sample container may hold clues as to how the Earth became habitable.

Ryugu is an example of a C-type or “carbonaceous” asteroid. These asteroids have undergone relatively little change since the start of the solar system, and are thought to contain hydrated minerals (minerals containing water in their structure) and possible organics. It is this class of asteroid that may have crashed into the early Earth and delivered the necessary tools for life to begin. Analysis of the Ryugu sample could therefore tell us about our own beginnings and how terrestrial planets develop habitable conditions.

Images before and after the first touchdown of Hayabusa2 on asteroid Ryugu, taken with CAM-H on February 21, 2019 (animation plays at 5x speed) (JAXA).

As the Hayabusa2 spacecraft drew near the Earth, five “trajectory control manoeuvres” (TCMs) were planned. The first four of these were designed to put the spacecraft onto a collision course with the Earth, aimed at the Woomera desert in Australia. The re-entry capsule would then be released, and the spacecraft would make a final manoeuvre to divert onto an orbit that swept past the Earth and back into deep space.

Despite the smooth progress so far, there were concerns. The capsule release mechanism had not been tested since launch six years previously and it was always possible that separation would fail.… Read more

The Faint Young Sun Paradox and Mars

This NASA image of Mars at sunset taken by the Spirit  rover, evokes the conditions on early Mars when the planet received only 70 percent of the of the solar energy that it does now.  (NASA/JPL/Texas A&M/Cornell)

When our sun was young, it was significantly less luminous and sent out significantly less warming energy than it does now.  Scientists estimate that 4 million years ago, when the sun and our solar system were 500 million years old, the energy that the sun produced and dispersed was about 75 percent of what it is today.

The paradox arises because during this time of the faint young sun Earth had liquid water on its surface and — as has been conclusively proven in recent years — so did Mars, which is 61 million miles further into space.  However difficult it is to explain the faint young sun problem as it relates to early Earth, it is far more difficult to explain for far more frigid Mars.

Yet many have tried.  And because the data is both limited and innately puzzling, the subject has been vigorously debated from a variety of different perspectives.  In 2018, the journal Nature Geoscience published an editorial on the state of that dispute titled “Mars at War.”

There are numerous point of (strenuous) disagreement, with the main ones involving whether early Mars was significantly more wet and warm than previously inferred, or whether it was essentially cold and arid with only brief interludes of warming.  The differences in interpretation also require different models for how the warming occurred.

Was there a greenhouse warming  effect produced by heat-retaining molecules in the atmosphere?  Was long-term volcanic activity the cause? Or perhaps meteor strikes?  Or heat from the interior of the planet?

All of these explanations are plausible and all may have played a role.  But that begs the question that has so energized Mars scientists since Mars orbiters and the Curiosity rover conclusively proved that surface water created early rivers and valley networks, lakes and perhaps an ocean.  To solve the “faint young sun” paradox as it played out on Mars,  a climate driver (or drivers) that produces significant amounts of heat is required.

Could the necessary warming be the result of radioactive elements in the Martian crust and mantle that decay and give off impressive amounts of heat when they do?

A team led by Lujendra Ojha, an assistant professor at Rutgers University, proposes in Science Advances that may well be the answer, or at least part of the answer.… Read more

How Radioactive Elements May Make Planets Suitable or Hostile to Life

An artist’s conception of a super Venus planet on the left and a super Earth on the right.  The question of what makes one planet habitable and one uninhabitable is a focus of many astrobiology researchers.  A new hypothesis looks at the presence of radioactive elements as an important factor in making a solar system habitable. (NASA/JPL-Caltech/Ames)

When describing exoplanets that are potentially promising candidates for life, scientists often use the terminology of the “habitable zone.”  This is a description of planets in orbit where temperatures, as predicted by the distance from the host star,  are not too cold for liquid water to exist on a planetary surface and also not to hot for all the water to burn off.

This planetary sweet spot, which not surprisingly Earth inhabits, is also more casually called the “Goldilocks zone” for exoplanets.

While there is certainly value to the habitable zone concept, there has also been scientific pushback to using the potential presence of liquid water as a primary or singular factor in predicting potential habitability.

There are just too many other factors that can play into habitability, some argue, and a focus on a planet’s distance from its host sun (and thus its temperature regime) is too narrow.  After all, several of the objects that just might support life in our own solar system are icy moons quite far from any solar system habitable zone.

With these concerns in the background, an interdisciplinary team of astrophysicists and planetary scientists at the University of California, Santa Cruz has begun to look at a source of heat in addition to suns and tidal forces that might play a role in making a planet habitable.

This source is the heat generated by the decay of long-lived radioactive elements such as uranium, thorium and potassium, which are found in stars and presumably on and in planets throughout the galaxies in greater or lesser amounts.

Using theory and modeling, they have concluded that the abundance of these radioactive elements in a planetary mantle can indeed give important insights into whether life might emerge there.

Supercomputer models of Earth’s magnetic field,  which is kept going thanks in part to the heat and subsequent convection produced by radioactive decay. (NASA)

Uranium is among the most widespread  elements on Earth — 500 times more common than gold It is present on the surface and in the mantle below. (Atomic Heritage Foundation.)

Read more

Strong Doubts Arise About the Reported Phosphine Biosignature in the Atmosphere of Venus

An artist’s depiction of Venus and, in the inset, phosphine molecules.
(© ESO/M. Kornmesser/L. Calçada & NASA/JPL-Caltech,)

What started as a stunning announcement that the chemical phosphine — a known byproduct of life — had been found in the clouds of Venus and could signal the presence of some lifeform has now been strongly critiqued by a number of groups of scientists.   As a result, there is growing doubt that the finding, published in the journal Nature Astronomy in September,  is accurate.

The latest critique, also submitted to Nature Astronomy but available in brief before publication, is led by NASA’s planetary scientist Geronimo Villaneuva and others at the Goddard Space Flight Center. They reanalyzed the data used to reach the conclusion that phosphine was present and concluded that the signal was misinterpreted as phosphine and most likely came instead from sulphur dioxide, which Venus’s atmosphere is known to contain in large amounts.

The title of their paper is “No phosphine in the atmosphere of Venus.”

Another paper led by Ignas Snellen from the Leiden Observatory came to a similar conclusion, but finding fault elsewhere. She and her team analyzed the data used in the initial research to see if cleaning up the noise with a 12-variable mathematic formula, as was used in the paper, could lead to incorrect results.

According to Snellan, using this formula actually gave the original team —  false results and they found “no statistical evidence for phosphine in the atmosphere of Venus.”

While this critical research does not on its own disprove that phosphine exists in Venus’ atmosphere, it clearly raises doubts about original team’s conclusions.

That original team was lead by Jane S. Greaves, a visiting scientist at the University of Cambridge when when she worked on the phosphine finding.  She herself has also has been unable to replicate the level of phosphine found by her team, and was a co-author on a paper that described that.   It is now almost impossible to collect new data because of the coronavirus pandemic.

 

Venus is roughly the size of Earth but much hotter due to its huge concentrations of carbon dioxide in the atmosphere.  (NASA)

This intense scrutiny continues as staff at the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, discovered a separate, unspecified issue in the data that were used to detect the phosphine. “There are some issues with interpretation that we are looking at,” says Dave Clements, an astrophysicist at Imperial College London and co-author of the original study.… Read more

New Discoveries of Water on the Sunlit Side of the Moon. Might the H2O Be Encased in Glass-like Beads?

This illustration highlights the moon’s Clavius Crater with an illustration depicting water trapped in the lunar soil there, along with an image of NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) that found sunlit lunar water. (NASA)

The search for water on the moon has produced a discovery of tiny molecule-sized perhaps widespread amounts of H20 in a sunlit lunar crater.

The water is not in a liquid or ice or gaseous form, but rather apparently contained (and protected) inside glass beads formed when micrometeorites hit the surface.

The detection was made using the Stratospheric Observatory for Infrared Astronomy (SOFIA), a high-flying modified airplane with an infrared telescope.

NASA scientists made clear that the lunar H2O in sunlight might prove to be too difficult to collect to be of use to astronauts, but future robotic and human missions on the lunar surface could also find more concentrated deposits now that they know some water is present.

“Prior to the SOFIA observations, we knew there was some kind of hydration” on the lunar surface said Casey Honniball, the lead author of a paper in the journal Nature Astronomy.  “But we didn’t know how much, if any, was actually water molecules – like we drink every day – or something more like drain cleaner.”

“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space,” said Honniball, who is now a postdoctoral fellow at NASA’s Goddard Space Flight Center. “Yet somehow we’re seeing it. Something is generating the water, and something must be trapping it there.”

An artist rendering of ater and its chemical precursors spraying out from minerals on the moon’s surface after a micrometeorite impact. Researchers have delved deeper into this process in the lab, taking the influence of solar wind into account. (NASA Goddard Conceptual Image Lab.)

Scientists have searched for water on the moon since Apollo days, and have known for some time that frozen water exists in some always-dark craters of the lunar south pole. Prior lunar missions have also detected hydrogen on sunlit surfaces, and it was initially thought to be in the form of hydroxyl (OH) rather then  water (H2O.)

SOFIA offered a new means of looking at the moon. Flying at altitudes of up to 45,000 feet, this modified Boeing 747SP jetliner with a 106-inch diameter telescope reaches above 99% of the water vapor in Earth’s atmosphere to get a clearer view of the infrared universe.… Read more

Captured on Oct. 20 during the OSIRIS-REx mission’s Touch-And-Go (TAG) sample collection, the NASA spacecraft approached and touches down on asteroid Bennu’s surface. The dramatic sampling event, a NASA first,  brought the spacecraft down to sample site Nightingale.  The team on Earth received confirmation of successful touchdown at 6:08 p.m. EDT. (NASA/Goddard/University of Arizona)

Over 200 million miles away,  NASA’s OSIRIS-REx spacecraft on Tuesday unfurled its robotic arm and descended to the surface of the asteroid Bennu.  It appeared to crush some rock as it touched down, quickly fired some nitrogen gas to kick up the sample and then after 5 or 6 seconds it flew away to safety after a back-away burn.

One day after the “tag,” NASA officials announced that the sample collection appeared to have been it to be a successful,  and they released images and video of the dramatic scoop.  The spacecraft touched down within three feet of the Nightingale target location and NASA officials said that most of the sample collection occurred in the first three seconds.

The sample will consist of grains of a surface that has experienced none of the ever-active geology on Earth,  no modifications caused by life,  and little of the erosion and weathering.  In other words, it will be a sample of the very early solar system from which our planet arose.

The asteroid visit is the first ever accomplished by NASA, following in the path set by the Japan Aerospace Exploration Agency (JAXA) and its two Hayabusa missions.

“This amazing first for NASA demonstrates how an incredible team from across the country came together and persevered through incredible challenges to expand the boundaries of knowledge,” said NASA Administrator Jim Bridenstine. “Our industry, academic, and international partners have made it possible to hold a piece of the most ancient solar system in our hands.”

Artist rendering for OSIRIS-REX spacxecrsft as it approaches the asteroid Bennu to collect a sample and quickly depart. The “tag” took place on Oct. 20. (NASA)

While it remains somewhat unclear how much sample was collected by OSIRIS-REx, the mission’s principal investigator,  Dante Lauretta of the University of Arizona, said he was optimistic.

The sampling mechanism touched down in part on a rock about 8 inches wide, something that could have prevented the gathering mechanism from pressing up properly against the surface.

“I must have watched about a hundred times last night,” Lauretta, said during a news conference on Wednesday.

Read more

Surprising Insights Into the Asteroid Bennu’s Past, as OSIRIS-REx Prepares For a Sample-Collecting “Tag”

Artist rendering of the OSIRIS-REx spacecraft as it will approach the asteroid Bennu to collect a sample of ancient, pristine solar system material. The  pick-up”tag” is scheduled for Oct. 20. (NASA Goddard Space Flight Center, University of Arizona)

Long before there was an Earth, asteroids large and small were orbiting our young sun.  Among them was one far enough out from the sun to contain water ice, as well as organic compounds with lots of carbon.  In its five billion years or so as an object,  the asteroid was hit and broken apart by other larger asteroids, probably grew some more as smaller asteroids hit it,  and then was smashed to bits again many millions of years ago.  Some of it might have even landed on Earth.

The product of this tumultuous early history is the asteroid now called Bennu, and the destination for NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) mission.  On October 20, the spacecraft will make its dramatic final descent, will touch the ground long enough to collect some samples of the surface, and then will in the months ahead return home with its prized catch.

The sample will consist of grains of a surface that have experienced none of the ever-active geology on Earth,  no modifications caused by life,  and little of the erosion and weathering.  In other words, it will be a sample of the very early solar system from which our planet arose.

“This will be our first chance to look at an ancient, carbon-rich environment – the most pristine example of the chemistry of the very early solar system,” said Daniel Glavin, an astrobiologist at NASA’s Space Flight Center and a co-investigator of the OSIRIS-REx team.  “Anything as ancient on early Earth would have been modified many times over.”

“But at Bennu we’ll see the solar system, and the Earth,  as it was chemically before all those changes took place.  This will be the kind of pristine pre-biotic chemistry that life emerged from.”

This image of Bennu was taken by the OSIRIS-REx spacecraft from a distance of around 50 miles (80 km).
(NASA/Goddard/University of Arizona)

Bennu is an unusual asteroid.  It orbits relatively close to Earth — rather than in the main asteroid belt between Mars and Jupiter — and that’s one of several main reasons why it was selected for a visit.  It is also an asteroid with significant amounts of primeval carbon and organics, which is gold for scientists eager to understand the early solar system, planet formation and the origin of life on Earth.… Read more

The Planet Larger Than Its Star

Artist animation of WD 1856 b orbiting the white dwarf. Due to the tiny size of the white dwarf and close orbit of the planet, the animation is to scale. The slightly inclined orbit means that the planet does not entirely block the white dwarf’s light as it transits (Tasker).

It has been an exciting month for planets. Just days after the announcement of a detection of phosphine in the clouds of Venus, another first in planet discoveries was declared. The new find is the first planet observed to be orbiting a white dwarf; a dead star that is much smaller than the planet it hosts.

Planet WD 1856+534 b was first spotted by the NASA’s Transiting Exoplanet Survey Satellite (TESS) and confirmed with a series of observations from ground-based telescopes. The results showed the light from a white dwarf being periodically dimmed by a staggering 56% for brief 8 minutes.

For comparison, one of the easiest exoplanet types to detect is a hot Jupiter that would typically cause a 1% dip in brightness of its star over a period of a few hours.

This suggested a Jupiter-sized planet was closely orbiting a white dwarf that was similar in size to the Earth. Light from the white dwarf is obscured each time the planet passes in front of (or transits) the dead star’s surface on its orbit. Interestingly, the light dip is shaped like the letter V, showing a gentle gradient decreasing and rising from the maximum occultation. The lack of a sharp drop in brightness implied the planet’s orbit was slightly inclined so that it grazed the white dwarf’s surface and only obscured part of the much smaller star.

Light dip (transit) observations of WD 1856 observed with the Gran Telescopio Canarias (GTC) in visible light. The red curve is the best-fitting models. The V-shape suggests the planet is grazing the white dwarf and does not obscure it completely (Vanderburg et al. 2020, Figure 1a).

Although certainly unusual, WD 1856 b is not the first planet known to orbit a smaller star. The first extrasolar planets to be discovered orbit another type of stellar remnant known as a neutron star. While white dwarfs typically have sizes similar to a terrestrial planet, neutron stars have city-sized diameters of order 10 km.

The fact both these cases involve dead stars is no coincidence. In order to orbit, the mass of the planet must be much less than that of the star.… Read more

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