Many Worlds

Tag: ALMA

Why Does Our Solar System Have No Super-Earths, and Other Questions for Comparative Planetology

December 1, 2021 / / 0 Comments

An artist’s impression of the exoplanet LHS 1140b, which orbits a red dwarf star 40 light-years from Earth. Using the European Southern Observatory’s telescope at La Silla, Chile, and other telescopes around the world, an international team of astronomers discovered this super-Earth orbiting in the habitable zone around the faint star LHS 1140. This world is a little larger and much more massive than the Earth. (ESO)

Before the explosion in discovery of extrasolar planets, the field of comparative planetology was pretty limited  — confined to examining the differences between planets in our solar system and how they may have come to pass.

But over the past quarter century, comparative planetology and the demographics of planets came to mean something quite different.  With so many planets now identified in so many solar systems, the comparisons became not just between one planet and another but also between one solar system and another.

And the big questions for scientists became the likes of:  How and why are the planetary makeups of distant solar systems often so different from our own and from each other; what does the presence  or absence of large planets in a solar system do to the distribution of smaller planets;  how large can a rocky planet can get before it turns to a gas giant planet; and on a more specific subject, why do some solar systems have hot Jupiters close to the host star and others have cold Jupiters much further out like our own

Another especially compelling question involves our own solar system, though as something of an outlier rather than a prototype.

That question involves the absence in our solar system of anything in the category of a “super-Earth” — a rocky or gaseous extrasolar planet with a mass greater than Earth’s but substantially below those of our solar system’s planets next in mass,  Uranus and Neptune.

The term “super-Earth” refers only to the mass and radii of the planet, and so does not imply anything about the surface conditions or habitability. But in the world of comparative planetology “super-Earths” are very important because they are among the most common sized exoplanets found so far and some do seem to have planetary characteristics associated with habitability.

Yet they do not exist in our solar system.  Why is that?

Artist rendition of Earth in comparison to one of the many super-Earth planets. (NASA)

In a recent article in The Astrophysical Journal Letters,  planetary demographer Gijs D.… Read more

Many Planets Form in a Soup of Life-Friendly Organic Compounds

October 14, 2021 / / 0 Comments

Artist’s depiction of a protoplanetary disk with young planets forming around a star. The right-side panel zooms in to show various organic molecules that are accreting onto a planet. (M.Weiss/Center for Astrophysics | Harvard & Smithsonian)

One of the more persuasive arguments in favor of the potential existence of life beyond Earth is that the well-known chemical building blocks of that life are found throughout the galaxy.  These chemical components aren’t all present in all examined solar systems and planets, but they are common and behave in ways familiar to scientists here.

And when it comes elements and compounds found on distant planets but not found here, there just aren’t many. That doesn’t mean they don’t exist — some unstable compounds in interstellar space, for instance — but rather that the cosmos holds many surprises but none have involved extraterrestrial elements or compounds near planets or stars.

This is in large part the result of how elements are formed in the universe.  Other than hydrogen and helium, all other elements are forged in the thermonuclear explosion of stars that have exhausted their supply of fuel.  These massive explosions (supernovae) then shoot the newly-formed elements out into space where they can and do collect in gas and dust clouds that will form other new stars.  They are spread throughout the disks that form around new stars and over time they become components of new planets in formation.

This galactic evolution includes the bonding together of carbon-based organic compounds — the building blocks of life as we know it.  They are an essential component to any theory of a planet’s habitability and,  while their presence in space and star nurseries has been known for some time,  they have remained a subject of great interest but limited detailed knowledge.

That is why an international team from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. set out to intensively study five disks forming around young stars to determine more precisely what organic compounds were present and available for objects developing into planets.

And the results are striking:  The abundance of organic material detected was 10 to 100 times more than expected.

“These planet-forming disks are teeming with organic molecules, some of which are implicated in the origins of life here on Earth,” said team leader Karin Öberg. “This is really exciting; the chemicals in each disk will ultimately affect the type of planets that form and determine whether or not the planets can host life.”… Read more

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

November 4, 2020 / / 2 Comments

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

Planets Still Forming Detected in a Protoplanetary Disk

June 15, 2018 / / 0 Comments

An artist rendering of infant star HD 163296 with three protoplanets forming in its disk  The planets were discovered using a new mode of detection — identifying unusual patterns in the flow of gas within a protoplanetary disk. (NRAO/AUI/NSF; S. Dagnello)

Just as the number of planets discovered outside our solar system is large and growing — more than 3,700 confirmed at last count — so too is the number of ingenious ways to find exoplanets ever on the rise.

The first exoplanets were found by measuring the “wobble” in their host stars caused by the gravitational pull of the planets, then came the transit technique that measured dips in the light from stars as planets passed in front of them, followed by the direct imaging of moving objects deemed to be planets, and numerous more.

A new technique can now be added to the toolkit, one that is useful only in specific galactic circumstances but is nonetheless ingenious and intriguing.

By detecting unusual patterns in the flow of gas within the protoplanetary disk of a young star, two teams of astronomers have confirmed the distinct, telltale hallmarks of newly formed planets orbiting the infant star.

In other words, the astronomers found planets in the process of being formed, circling a star very early in its life cycle.

These results came thanks to the Atacama Large Millimeter/submillimeter Array (ALMA), and are presented in a pair of papers appearing in the Astrophysical Journal Letters.

Richard Teague, an astronomer at the University of Michigan and principal author on one of the papers, said that his team looked at “the localized, small-scale motion of gas in a star’s protoplanetary disk. This entirely new approach could uncover some of the youngest planets in our galaxy, all thanks to the high-resolution images coming from ALMA.”

ALMA image of the protoplanetary disk surrounding the young star HD 163296 as seen in dust. ( ALMA: ESO/NAOJ/NRAO; A. Isella; B. Saxton NRAO/AUI/NSF.

To make their respective discoveries, each team analyzed the data from various ALMA observations of the young star HD 163296, which is about 4 million years old and located about 330 light-years from Earth in the direction of the constellation Sagittarius.

Rather than focusing on the dust within the disk, which was clearly imaged in an earlier ALMA observation, the astronomers instead studied the distribution and motion of carbon monoxide (CO) gas throughout the disk.

As explained in a release from the National Radio Astronomy Observatory, which manages the American operations of the multi-national ALMA, molecules of carbon monoxide naturally emit a very distinctive millimeter-wavelength light that ALMA can observe.

… Read more

What Astrochemistry is Telling Us

June 7, 2017 / / 0 Comments

This image shows the Rho Ophiuchi region of star formation where methyl isocyanate was detected.  The insert shows the molecular structure of this chemical, an important precursor for life’s chemical building blocks. ESO/Digitized Sky Survey 2/L. Calçada

Sometimes lost in the discussion of exoplanets and habitability is where the potential building blocks of life might come from and how they got there.

Yes, hydrogen and water and methane and carbon and nitrogen have been found in abundance around the cosmos, but how about the larger and more esoteric compounds needed for life to emerge?  The precursor compounds to amino acids and nucleobases, for instance. Are they formed in space, too.

Some have indeed been identified around young stars or in star-formation regions, but much of what we know about complex molecules in space comes via meteorites and comets.

The Philae lander, for instance, identified 16 organic compounds on the Churyumov-Gerasimenko comet in 2015, including four never-before detected on comets. Some of these compounds play a key role in the prebiotic synthesis of amino acids, sugars and nucleobases — the ingredients for life.

Now an additional and significant precursor compound has been detected around sun-like stars in the very early stage of their formation.  The chemical is methyl isocyanate, and it is an important building block of life.

The detection was made by two teams at the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope, high in the Chilean desert.  The researchers described their detection as the first one of this prebiotic molecule around a solar-type protostar, the type from which our solar system evolved.

“We are particularly excited about the result because these protostars are very similar to the Sun at the beginning of its lifetime, with the sort of conditions that are well suited for Earth-sized planets to form,” said Rafael Martín-Doménech of the Centro de Astrobiología in Madrid and Víctor M. Rivilla of the Osservatorio Astrofisico di Arcetri in Florence. They were lead authors of one of the two papers published on the subject by the Royal Astronomical Society.

“By finding prebiotic molecules in this study, we may now have another piece of the puzzle in understanding how life came about on our planet.”

The Atacama Large Millimeter/submillimeter Array (ALMA) is a partnership between nations in Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is the largest ground-based astronomical observatory in existence, and it is located on one of the driest spots on Earth.

… Read more

Elegant Image of Icy Disk Around The Young Fomalhaut System

May 19, 2017 / / 0 Comments

Composite image of the Fomalhaut star system. The ALMA data, shown in orange, reveal the distant and eccentric debris disk in never-before-seen detail. The central dot is the unresolved emission from the star, which is about twice the mass of our sun. Optical data from the Hubble Space Telescope is in blue; the dark region was a blocked by an internal coronagraph which filtered out the otherwise overwhelming light of the central star.  ALMA (ESO/NAOJ/NRAO), M. MacGregor; NASA/ESA Hubble, P. Kalas; B. Saxton (NRAO/AUI/NSF)

An international team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) has made the first complete millimeter-wavelength image of the ring of dusty debris surrounding the young star Fomalhaut. This well-defined band of rubble and gas is likely the result of comets smashing together near the outer edges of a planetary system 25 light-years from Earth.

Earlier ALMA observations of Fomalhaut — taken in 2012 when the telescope was still under construction – revealed only about one half of the debris disk. Though this first image was merely a test of ALMA’s initial capabilities, it nonetheless provided tantalizing hints about the nature and possible origin of the disk.

The new ALMA observations offer a complete view of this glowing band of debris and also suggest that there are chemical similarities between its icy contents and comets in our own solar system.

“ALMA has given us this staggeringly clear image of a fully formed debris disk,” said Meredith MacGregor, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and lead author on one of two papers accepted for publication in the Astrophysical Journal describing these observations.

“We can finally see the well-defined shape of the disk, which may tell us a great deal about the underlying planetary system responsible for its highly distinctive appearance.”

Fomalhaut is a relatively nearby star system with harbors of the first planets to be directly imaged by a space telescope.  In all, about 20 star systems have exoplanets that have been imaged directly.

The entire Formalhaut system is approximately 440 million years old, or about one-tenth the age of our solar system.

The Hubble images were taken with the Space Telescope Imaging Spectrograph in 2010 and 2012. This false-color composite image, taken with the Hubble Space Telescope, reveals the orbital motion of the planet Fomalhaut b. Based on these observations, astronomers calculated that the planet is in a 2,000-year-long, highly elliptical orbit.

… Read more

© 2023 Many Worlds

Theme by Anders Noren — Up ↑