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The Directly Imaged World Around α Centauri?

Optical and X-ray (cut-out) image of the Alpha Centauri binary stars (Optical: Zdenek Bardon; X-ray: NASA/CXC/Univ. of Colorado/T. Ayres et al.)

There is something terribly exciting about actually seeing an exoplanet. While we have discovered over 4,000 planets outside the solar system, the majority of these worlds have been identified through their influence on their star, either via a dimming of the star’s light as the planet transits across its surface, or the wobble of the star from the planet’s gravitational pull. These are incredibly powerful techniques for planet hunting, but neither allow us to actually lay eyes on the planet itself.

The method to actually see a planet is known as “direct imaging” and it is a tricky process, as the star’s light can easily overwhelm any radiation coming from the smaller, cooler planet. Exoplanet imagining has therefore focused on young Jupiter-sized worlds orbiting far from the powerful lighthouse of the star. These planets are large and their recent formation has left them packed with heat, with temperatures around 1340°F (727°C). Such hot houses emit thermal radiation at wavelengths around 5 microns, so most of the instruments dedicated to capturing planet pictures operate around this wavelength range.

Direct imaging of exoplanets is difficult, and so far has been mainly restricted to young, massive planets. This amazing animation of four planets more massive than Jupiter orbiting the young star HR 8799 includes images taken over seven years at the W.M. Keck observatory in Hawaii. (Jason Wang and Christian Marois)

However, these wavelengths are a bad choice if you want to try imaging an Earth-like world. As an evolved planet on a temperate orbit, thermal emission from a planet like our own is longer at about 10 – 20 microns. This is an awkward wavelength for observations from the Earth, as the Earth’s own thermal emission can swamp the distant signal of the planet.

Yet, being able to directly image temperate planets is an important technique for studying possible habitable worlds. As you move away from the star, the chances of the planet’s orbit transiting across the star’s surface from our view from Earth decreases. For a planet on a similar orbit to the Earth around a sun-like star, the probability is less than 0.5%. The only way to study many of these worlds may be if we can see them directly, and space-based observatories have been generally seen as the path to this kind of imaging.… Read more

NASA’s Perseverance Rover Lands on Mars — The Third Martian Arrival in a Week

This true-color Mars globe includes Terra Meridiani, the region where NASA’s Opportunity rover explored from 2004 to 2018.  Two more Mars rovers — one from NASA and the other from China — are scheduled to land this week and then later in the year. (NASA/Greg Shirah)

Mars is receiving visitors these days.  Quite a few of them.

The most prominent visitor is NASA’s Perseverance rover,  which made a difficult but smooth precision landing at 3.55 ET  this afternoon.

The rover now sits in Jezero Crater, in an area that clearly once had lots of water flowing.   The site was selected, in part, because the Perseverance rover’s official mission includes — for the first time since the mid 1970s — an effort to find signs of long ago life.

Perseverance will join the Curiosity rover on Mars, that pioneering machine that has revolutionized our understanding of the planet since it landed in 2012  The Curiosity and Perseverance rovers are similar in design but carry different instruments with different goals.

A key difference:  Curiosity was tasked with determining whether Mars had once been habitable and found that it definitely had been, with flowing rivers, large lakes and necessary-for-life organic compounds.  Perseverance will take another scientific step forward and search for signs that Mars actually was once inhabited.

Perseverance also joins China’s Tianwen-1 (“heavenly questions”) probe,  which went into orbit around Mars last week.  It is the first Chinese spacecraft to arrive at Mars, and later this spring or summer the Chinese space agency will attempt to land a rover as well on the planet’s northern plains..

And then there’s the Hope spacecraft which entered into Mars orbit last week as well.  Launched by the United Arab Emirates, it was placed in a wide orbit so it could study the planet’s weather and climate systems, which means it also can see the full planet in one view.

These spacecraft will join several others on or orbiting Mars, making this by far the busiest time ever for exploration of Mars — a real milestone.

NASA’s Perseverance rover will land in Jezero Crater. This image was produced using instruments on NASA’s Mars Reconnaissance Orbiter, which helps identify potential landing sites for future missions. On ancient Mars, water carved channels and transported sediments to form fans and deltas within lake basins, as is clearly visible at here at Jezaro Crater (NASA/JPL-Caltech/ASU)

That the Perseverance mission has a formal goal of searching for ancient signs of life is a big deal, and involves a lot of history.… Read more

New Insights Into How Earth Got Its Nitrogen

An artist’s conception shows a protoplanetary disk of dust and gas around a young star. New research by Rice University shows that Earth’s nitrogen came from both inner and outer regions of the disk that formed our solar system, contrary to earlier theory.  (NASA/JPL-Caltech)

Scientists have long held that many of the important compounds and elements that make life possible on Earth arrived here after the planet was formed and was orbiting the sun.  These molecules came via meteorites and comets, it was thought,  from the colder regions beyond Jupiter.

But in a challenge to that long-accepted view, a team from Rice University has found isotopic signatures of nitrogen from both the inner and the outer disk in iron meteorites that fell to Earth.  What this strongly suggests is that the seeds of rocky, inner solar system planets such as Earth were bathed in  dust that contained nitrogen and other volatiles, and the growing planet kept some of that “local” material.

“Our work completely changes the current narrative,” said Rice University graduate student and lead author Damanveer Grewal. “We show that the volatile elements were present in the inner disk dust, probably in the form of refractory (non-gaseous) organics, from the very beginning. This means that contrary to current understanding, the seeds of the present-day rocky planets — including Earth — were not volatile-free.”

The solar protoplanetary disk was separated into two reservoirs, with the inner solar system material having a lower concentration of nitrogen-15 and the outer solar system material being nitrogen-15 rich. The nitrogen isotope composition of present-day Earth lies in between, according to a new Rice University study that shows it came from both reservoirs. (Credit: Illustration by Amrita P. Vyas)

This work helped settle a prolonged debate over the origin of life-essential volatile elements — such as hydrogen, water, carbon dioxide, methane, nitrogen, ammonia — on Earth and other rocky bodies in the solar system.

“Researchers have always thought that the inner part of the solar system, within Jupiter’s orbit, was too hot for nitrogen and other volatile elements to condense as solids, meaning that volatile elements in the inner disk were only in the gas phase,” Grewal said.

Because the seeds of present-day rocky planets, also known as protoplanets, grew in the inner disk by accreting locally sourced dust, he said it appeared they did not contain nitrogen or other volatiles because of the high temperatures, necessitating their delivery from the outer solar system.… Read more

How to Predict the Make-Up of Rocky Exoplanets Too Small and Distant to Directly Observe

The seven planets of the Trappist-1 solar system.  The first planets were discovered five years ago and others in 2017.  Trappist-1 is a dream system for researchers to study because it includes so many rocky planets.  The planets do, however, orbit very close to a relatively small and cool Red Dwarf star, which makes the system and its potential for habitability different than if they orbited a sun-like star. (NASA)

In trying to tease out what a planet is made of, its density is of great importance.   Scientists can use that measure  of density — the amount of matter contained in a given volume — to determine what ratio of a planet is likely is gas, or water, or rocks, or rocks and iron and more. They can even help determine if the planet has a central core.

So determining the density of exoplanets is a high priority and one that has been especially important for the Trappist-1 solar system, the amazing collection of seven “Earth-sized” rocky planets orbiting a Red Dwarf star some 40 light years away.

The Trappist-1 planets have been a major focus of study since its first planets were discovered in 2016, and now a new and rather surprising finding about the density of the planets has been accepted for publication in the Planetary Science Journal .  While the planets are somewhat different sizes, they appear to be all almost the exact same density.  This provides a goldmine of information for scientists.

Equally exciting, while the seven Trappist-1 planets have similar densities, they are 8% less dense than they would be if they had the same chemical composition as our planet.  It may not seem like a lot, but to astrophysicists it is.

“This is the information we needed to make hypotheses about their composition and understand how these planets differ from the rocky planets in our solar system,” said lead author Eric Agol of the University of Washington.

What Agol considers the team’s most robust conclusions:  The Trappist-1 planets have a “common make-up” just as the rocky planets in our solar system do, but are nonetheless in some significant ways different from our rocky planets.  “TRAPPIST-1 has a different ‘recipe’ for forming terrestrial planets, and a more uniform recipe as well,” he told me.

A planet’s density is determined not just by its composition, but also by its size: Gravity compresses the material a planet is made of, increasing the planet’s density.

Read more

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

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