Astronomy and Planetary Science Thread

[Flyaway]

Have We Found Planet 9?

View: https://youtu.be/VQqOo2Kfzbs

 

[Flyaway]

His data suggest the new world would be three to five times more massive than the Earth, and orbiting the Sun at about 225 times the distance of our own planet.

Michael Rowan-Robinson, Emeritus professor of astrophysics at Imperial College London, and a former President of the Royal Astronomical Society, found his candidate for a new world in historic observations made by an early space telescope.

The Infrared Astronomical Satellite (IRAS) was launched in 1983 as the first orbiting observatory to look at the entire night sky in the infrared region of the spectrum, which lies just beyond the rainbow of visible light.

Over ten months, the mission observed more than a quarter of a million infrared sources in the sky, by detecting their heat against the cold sky background.

In a research paper describing his search for Planet 9, the professor admits that the observations are not of high quality and were made in a region of sky full of filaments of galactic gas known as cirrus because of their cloud-like nature.

He also concedes that a more recent comprehensive survey of the night sky by Pan-STARRS telescopes in Hawaii have failed to record the object, suggesting it is not real.

Planetary scientist Professor Mike Brown, who rejoices under the Twitter handle @plutokiller, and has been making his own search for another planet, tweeted: “The candidate is on an orbit utterly inconsistent with our predictions for Planet Nine, and would not be capable of gravitationally perturbing the distant Solar System in the ways that we have suggested. But, of course, that doesn’t mean it isn’t real!

“It just means that it would be a serendipitous discovery of something while searching for Planet Nine. Pluto happened the same way. Tombaugh was searching for Lowell’s Planet X (which didn’t exist) and accidentally found Pluto. Pluto was not the predicted Planet X.”

Professor finds possible ninth planet in our Solar System - Skymania

A leading British astronomer believes he has found possible evidence of a ninth planet in the Solar System.

www.skymania.com

 

[Flyaway]

Black Hole Discovered in Galaxy Next Door (ESOcast 245 light):

View: https://youtu.be/qW-HXYXYybk


For the first time, astronomers have discovered a small black hole outside the Milky Way by looking at how it influences the motion of a star in its close vicinity. This video summarises the discovery.

 

[Nik]

Slightly tangential, other than spotting a transiting planet, which usually constrains much of that system's orbital plane, there seems no practicable way to determine this...

Hence exo-planet masses found by 'doppler' come as 'Sin(i)'. Which may mean a fairly wide range...

My specific interest is Tau Ceti (f), where the Sin(i) problem means it could mass anywhere between a super-earth / water planet and a full-on sub-neptune. Sadly, ~35º angle of dust disk in outer system is no guarantee that inner system, with 'f', has same alignment...

Tau Ceti f - Wikipedia

en.wikipedia.org

 

[publiusr]

Gliese 710 has my attention. Every update shoves that fly-by closer. In THE STARFLIGHT HANDBOOK they call it DM 61 366...or is that another star?

 

[Flyaway]

On Thursday, the National Academies of Science released the latest Decadal Survey, which the astronomy industry uses to help guide funding decisions. While the survey doesn't guarantee funding, it's highly influential with NASA and the National Science Foundation (NSF), which fund most of the astronomy research in the US.

The latest iteration lays out a few scientific priorities, including the study of the formation and evolution of galaxies and exosolar systems. And it also suggests which hardware would be required to get the data we need for those studies. In this case, that involves the next of NASA's Great Observatories: a Webb-scale space telescope that is sensitive to wavelengths from UV to infrared.

New astronomy roadmap calls for huge, broad-spectrum space telescope

The decadal survey is a highly influential 10-year plan for what should come next.

arstechnica.com

Here’s the report itself:

Pathways to Discovery in Astronomy and Astrophysics for the 2020s | The National Academies Press

Read online, download a free PDF, or order a copy in print or as an eBook.

www.nap.edu

 

[publiusr]

Thanks for that.

 

[Flyaway]

A mysterious ‘superbubble’ carved in the heart of a glowing emission nebula

A mysterious ‘superbubble’ carved in the heart of a glowing emission nebula – Astronomy Now

astronomynow.com

 

[Flyaway]

It seems that the search for life on Mars could easily be misled by geological processes.

False biosignatures on Mars: anticipating ambiguity

Abstract

It is often acknowledged that the search for life on Mars might produce false positive results, particularly via the detection of objects, patterns or substances that resemble the products of life in some way but are not biogenic. The success of major current and forthcoming rover missions now calls for significant efforts to mitigate this risk. Here, we review known processes that could have generated false biosignatures on early Mars. These examples are known largely from serendipitous discoveries rather than systematic research and remain poorly understood; they probably represent only a small subset of relevant phenomena. These phenomena tend to be driven by kinetic processes far from thermodynamic equilibrium, often in the presence of liquid water and organic matter, conditions similar to those that can actually give rise to, and support, life. We propose that strategies for assessing candidate biosignatures on Mars could be improved by new knowledge on the physics and chemistry of abiotic self-organization in geological systems. We conclude by calling for new interdisciplinary research to determine how false biosignatures may arise, focusing on geological materials, conditions and spatiotemporal scales relevant to the detection of life on Mars, as well as the early Earth and other planetary bodies.

Lyell Collection

 

[Grey Havoc]

Longest partial lunar eclipse in nearly 600 years coming tonight

The longest partial lunar eclipse in nearly 600 years will grace the night sky late Thursday night and early Friday morning across the entire country.

www.yahoo.com

The longest lunar eclipse in centuries will happen this week, NASA says. What to know

You can see the longest partial lunar eclipse in hundreds of years this week.

www.bakersfield.com

 

[Grey Havoc]

Harvard Astronomers Challenge Theory That 'Oumuamua Was a Nitrogen Iceberg - Slashdot

"Although Oumuamua probably isn't some probe looking for humpbacked whales," writes Slashdot reader alaskana98, "it does continue to deliver plenty of intrigue — and controversy — for those astronomy buffs out there. "In the latest move in the war on who gets to define what exactly OuM...

science.slashdot.org

 

[publiusr]

I’m thinking that could be a shard of some extrasolar Half-Dome batholith…maybe a Ship Rock type volcanic neck/pipe that spalled off a planetary collision that could keep an elongated shape. A Vasquez Rocks type sedimentary layer is less likely to have survived than a granite shard.

 

[Flyaway]

Scientists recently added a whopping 301 newly validated exoplanets to the total exoplanet tally. The throng of planets is the latest to join the 4,569 already validated planets orbiting a multitude of distant stars. How did scientists discover such a huge number of planets, seemingly all at once? The answer lies with a new deep neural network called ExoMiner.

New deep learning method adds 301 planets to Kepler's total count

Scientists recently added a whopping 301 newly validated exoplanets to the total exoplanet tally. The throng of planets is the latest to join the 4,569 already validated planets orbiting a multitude of distant stars. How did scientists discover such a huge number of planets, seemingly all at...

phys.org

 

[Flyaway]

An upper limit on late accretion and water delivery in the TRAPPIST-1 exoplanet system

Abstract
The TRAPPIST-1 system contains seven roughly Earth-sized planets locked in a multiresonant orbital configuration1,2, which has enabled precise measurements of the planets’ masses and constrained their compositions3. Here we use the system’s fragile orbital structure to place robust upper limits on the planets’ bombardment histories. We use N-body simulations to show how perturbations from additional objects can break the multiresonant configuration by either triggering dynamical instability or simply removing the planets from resonance. The planets cannot have interacted with more than ~5% of one Earth mass (M⊕) in planetesimals—or a single rogue planet more massive than Earth’s Moon—without disrupting their resonant orbital structure. This implies an upper limit of 10−4 M⊕ to 10−2 M⊕ of late accretion on each planet since the dispersal of the system’s gaseous disk. This is comparable to (or less than) the late accretion on Earth after the Moon-forming impact4,5, and demonstrates that the growth of the TRAPPIST-1 planets was complete in just a few million years, roughly an order of magnitude faster than that of the Earth6,7. Our results imply that any large water reservoirs on the TRAPPIST-1 planets must have been incorporated during their formation in the gaseous disk.

An upper limit on late accretion and water delivery in the TRAPPIST-1 exoplanet system - Nature Astronomy

The resonant chain of the TRAPPIST-1 planets is dynamically fragile, as small perturbations during its lifetime would have disrupted it. N-body simulations show that the system could not have interacted with more than 0.05 Earth masses of material after its formation. Thus, any water in the...

www.nature.com

Source: https://phys.org/news/2021-11-orbital-harmony-limits-late-trappist-.amp

 

[Flyaway]

Planet 9 Possibly Found With Prof. Michael Rowan-Robinson:

View: https://youtu.be/U8p0baDb24Q

 

[Richard N]

The Dancing Auroras of Saturn

https://twitter.com/x/status/1463911105172934658

View: https://twitter.com/konstructivizm/status/1463911105172934658?s=20

 

[Richard N]

Jupiter's moon Io--I'd like to see that in my night sky!

https://twitter.com/x/status/1462052625915031566

View: https://twitter.com/latestinspace/status/1462052625915031566/photo/1

 

[Flyaway]

The HD 137496 system: A dense, hot super-Mercury and a cold Jupiter

Most of the currently known planets are small worlds with radii between that of the Earth and that of Neptune. The characterization of planets in this regime shows a large diversity in compositions and system architectures, with distributions hinting at a multitude of formation and evolution scenarios. Using photometry from the K2 satellite and radial velocities measured with the HARPS and CORALIE spectrographs, we searched for planets around the bright and slightly evolved Sun-like star HD 137496. We precisely estimated the stellar parameters, M∗ = 1.035 +/- 0.022 M⊙, R∗ = 1.587 +/- 0.028 R⊙, Teff = 5799 +/- 61 K, together with the chemical composition of the slightly evolved star. We detect two planets orbiting HD 137496. The inner planet, HD 137496 b, is a super-Mercury (an Earth-sized planet with the density of Mercury) with a mass of Mb = 4.04 +/- 0.55 M⊕, a radius of Rb=1.31+0.06−0.05R⊕, and a density of ρb=10.49+2.08−1.82 gcm−3. With an interior modeling analysis, we find that the planet is composed mainly of iron, with the core representing over 70% of the planet's mass (Mcore/Mtotal=0.73+0.11−0.12). The outer planet, HD 137496 c, is an eccentric (e = 0.477 +/- 0.004), long period (P = 479.9+1.0−1.1 days) giant planet (Mcsinic = 7.66 +/- 0.11 MJup) for which we do not detect a transit. HD 137496 b is one of the few super-Mercuries detected to date. The accurate characterization reported here enhances its role as a key target to better understand the formation and evolution of planetary systems. The detection of an eccentric long period giant companion also reinforces the link between the presence of small transiting inner planets and long period gas giants.

[2111.08764] The HD 137496 system: A dense, hot super-Mercury and a cold Jupiter

 

[Rhinocrates]

News about the TRAPPIST-1 system. Essentially, it's unlikely that there was significant late bombardment delivering water to the planets as they seem to have formed very quickly and any major impacts would have disrupted the delicate orbital resonance of the planets.

A couple of caveats, maybe: they may have migrated into a resonant arrangement rather than formed in one and the density of some of the planets suggests that they could be very wet.

Orbital harmony limits late arrival of water on TRAPPIST-1 planets

Seven Earth-sized planets orbit the star TRAPPIST-1 in near-perfect harmony, and U.S. and European researchers have used that harmony to determine how much physical abuse the planets could have withstood in their infancy.

news.rice.edu

https://www.nature.com/articles/s41550-021-01518-6 (abstract only - the rest is paywalled)

From the vault: Exoplanets dodge bombardment in their infancy

New research has used the harmonious orbits of the TRAPPIST-1 exoplanets to determine how much bombardment they withstood in their infancy.

cosmosmagazine.com

Orbital Harmony of TRAPPIST-1 Planets Could Survive Only Limited Early Bombardment

Fragile orbits of seven exoplanets limit late arrival of water. Seven Earth-sized planets orbit the star TRAPPIST-1 in near-perfect harmony, and U.S. and European researchers have used that harmony to determine how much physical abuse the planets could have withstood in their infancy. “After r

scitechdaily.com

Referring to composition:

The seven rocky planets of TRAPPIST-1 seem to have very similar compositions

Precise measurements reveal that the exoplanets of the system discovered by ULiège researchers have remarkably similar densities, which provides new clues about their compositions.

www.news.uliege.be

They may be highly oxidised, or

The third hypothesis put forward by the researchers is that the planets are enriched with water compared to the Earth.

 

[jeffb]

That's interesting, looks like they've adjusted some of the density numbers for the Trappist-1 planets as well as Trappist-1's brightness.

 

[jeffb]

A possible future tourist destination and only 12 parsecs away...

 

[Rhinocrates]

That's interesting, looks like they've adjusted some of the density numbers for the Trappist-1 planets as well as Trappist-1's brightness.

Interesting... tho' the density of Mercury seems low in that diagram.

Fingers crossed for the Webb launch to see if there's any atmospheric water vapour.

The authors of the study proposing an early limit to water delivery did say that they had some pretty big error bars.* At least exoplanetology is always delivering surprises.

*A joke told about cosmologists is that they put error bars on the exponents.

 

[jeffb]

That's interesting, looks like they've adjusted some of the density numbers for the Trappist-1 planets as well as Trappist-1's brightness.

Interesting...

Fingers crossed for the Webb launch to see if there's any atmospheric water vapour.

The authors of the study proposing an early limit to water delivery did say that they had some pretty big error bars.* At least exoplanetology is always delivering surprises.

*A joke told about cosmologists is that they put error bars on the exponents.

Please don't mention the Webb, you'll jinx it...more.
At least touch wood or throw salt over your shoulder just in case. (Me? Superstitious? Nah)

 

[Rhinocrates]

That's interesting, looks like they've adjusted some of the density numbers for the Trappist-1 planets as well as Trappist-1's brightness.

Interesting...

Fingers crossed for the Webb launch to see if there's any atmospheric water vapour.

The authors of the study proposing an early limit to water delivery did say that they had some pretty big error bars.* At least exoplanetology is always delivering surprises.

*A joke told about cosmologists is that they put error bars on the exponents.

Please don't mention the Webb, you'll jinx it...more.
At least touch wood or throw salt over your shoulder just in case. (Me? Superstitious? Nah)

Ah yes, it's become 'The Scottish Play' of astronomy.

 

[Flyaway]

News about the TRAPPIST-1 system. Essentially, it's unlikely that there was significant late bombardment delivering water to the planets as they seem to have formed very quickly and any major impacts would have disrupted the delicate orbital resonance of the planets.

A couple of caveats, maybe: they may have migrated into a resonant arrangement rather than formed in one and the density of some of the planets suggests that they could be very wet.

Orbital harmony limits late arrival of water on TRAPPIST-1 planets

Seven Earth-sized planets orbit the star TRAPPIST-1 in near-perfect harmony, and U.S. and European researchers have used that harmony to determine how much physical abuse the planets could have withstood in their infancy.

news.rice.edu

https://www.nature.com/articles/s41550-021-01518-6 (abstract only - the rest is paywalled)

From the vault: Exoplanets dodge bombardment in their infancy

New research has used the harmonious orbits of the TRAPPIST-1 exoplanets to determine how much bombardment they withstood in their infancy.

cosmosmagazine.com

Orbital Harmony of TRAPPIST-1 Planets Could Survive Only Limited Early Bombardment

Fragile orbits of seven exoplanets limit late arrival of water. Seven Earth-sized planets orbit the star TRAPPIST-1 in near-perfect harmony, and U.S. and European researchers have used that harmony to determine how much physical abuse the planets could have withstood in their infancy. “After r

scitechdaily.com

Referring to composition:

The seven rocky planets of TRAPPIST-1 seem to have very similar compositions

Precise measurements reveal that the exoplanets of the system discovered by ULiège researchers have remarkably similar densities, which provides new clues about their compositions.

www.news.uliege.be

They may be highly oxidised, or

The third hypothesis put forward by the researchers is that the planets are enriched with water compared to the Earth.

See my post #334 above already covered this.

 

[Flyaway]

Gaia EDR3 proper motions of Milky Way dwarfs. II: Velocities, Total Energy and Angular Momentum​

Here we show that precise Gaia EDR3 proper motions have provided robust estimates of 3D velocities, angular momentum and total energy for 40 Milky Way dwarfs. The results are statistically robust and are independent of the Milky Way mass profile. Dwarfs do not behave like long-lived satellites of the Milky Way because of their excessively large velocities, angular momenta, and total energies. Comparing them to other MW halo population, we find that many are at first passage, ≤ 2 Gyr ago, i.e., more recently than the passage of Sagittarius, ∼ 4-5 Gyr ago. We suggest that this is in agreement with the stellar populations of all dwarfs, for which we find that a small fraction of young stars cannot be excluded. We also find that dwarf radial velocities contribute too little to their kinetic energy when compared to satellite systems with motions only regulated by gravity, and some other mechanism must be at work such as ram pressure. The latter may have preferentially reduced radial velocities when dwarf progenitors entered the halo until they lost their gas. It could also explain why most dwarfs lie near their pericenter. We also discover a novel large scale structure perpendicular to the Milky Way disk, which is made by 20% of dwarfs orbiting or counter orbiting with the Sagittarius dwarf.

[2109.11557] Gaia EDR3 proper motions of Milky Way dwarfs. II: Velocities, Total Energy and Angular Momentum

 

[Flyaway]

My bolding. As it says further in the article even the Large Magellanic Cloud is not really a satellite galaxy.

And so, in the traditional view that the Milky Way’s dwarfs were satellite galaxies that had been in orbit for many billions of years, it was assumed that they must be dominated by dark matter to balance the Milky Way’s tidal force and keep them intact. The fact that Gaia has revealed that most of the dwarf galaxies are circling the Milky Way for the first time means that they do not necessarily need to include any dark matter at all, and we must re-assess whether these systems are in balance or rather in the process of destruction.

Gaia reveals that most Milky Way companion galaxies are newcomers to our corner of space

Data from ESA’s Gaia mission is re-writing the history of our galaxy, the Milky Way. What had traditionally been thought of as satellite galaxies to the Milky Way are now revealed to be mostly newcomers to our galactic environment.

www.esa.int

 

[FighterJock]

My bolding. As it says further in the article even the Large Magellanic Cloud is not really a satellite galaxy.

And so, in the traditional view that the Milky Way’s dwarfs were satellite galaxies that had been in orbit for many billions of years, it was assumed that they must be dominated by dark matter to balance the Milky Way’s tidal force and keep them intact. The fact that Gaia has revealed that most of the dwarf galaxies are circling the Milky Way for the first time means that they do not necessarily need to include any dark matter at all, and we must re-assess whether these systems are in balance or rather in the process of destruction.

Gaia reveals that most Milky Way companion galaxies are newcomers to our corner of space

Data from ESA’s Gaia mission is re-writing the history of our galaxy, the Milky Way. What had traditionally been thought of as satellite galaxies to the Milky Way are now revealed to be mostly newcomers to our galactic environment.

www.esa.int

Looks like a complete rewriting of astronomy books is in order after that new news from Gaia.

 

[Flyaway]

My bolding. As it says further in the article even the Large Magellanic Cloud is not really a satellite galaxy.

And so, in the traditional view that the Milky Way’s dwarfs were satellite galaxies that had been in orbit for many billions of years, it was assumed that they must be dominated by dark matter to balance the Milky Way’s tidal force and keep them intact. The fact that Gaia has revealed that most of the dwarf galaxies are circling the Milky Way for the first time means that they do not necessarily need to include any dark matter at all, and we must re-assess whether these systems are in balance or rather in the process of destruction.

Gaia reveals that most Milky Way companion galaxies are newcomers to our corner of space

Data from ESA’s Gaia mission is re-writing the history of our galaxy, the Milky Way. What had traditionally been thought of as satellite galaxies to the Milky Way are now revealed to be mostly newcomers to our galactic environment.

www.esa.int

Looks like a complete rewriting of astronomy books is in order after that new news from Gaia.

Things is does this result copy across to other galaxies as that would undermine the theory of Dark Matter I would have thought.

 

[FighterJock]

My bolding. As it says further in the article even the Large Magellanic Cloud is not really a satellite galaxy.

And so, in the traditional view that the Milky Way’s dwarfs were satellite galaxies that had been in orbit for many billions of years, it was assumed that they must be dominated by dark matter to balance the Milky Way’s tidal force and keep them intact. The fact that Gaia has revealed that most of the dwarf galaxies are circling the Milky Way for the first time means that they do not necessarily need to include any dark matter at all, and we must re-assess whether these systems are in balance or rather in the process of destruction.

Gaia reveals that most Milky Way companion galaxies are newcomers to our corner of space

Data from ESA’s Gaia mission is re-writing the history of our galaxy, the Milky Way. What had traditionally been thought of as satellite galaxies to the Milky Way are now revealed to be mostly newcomers to our galactic environment.

www.esa.int

Looks like a complete rewriting of astronomy books is in order after that new news from Gaia.

Things is does this result copy across to other galaxies as that would undermine the theory of Dark Matter I would have thought.

Try to explain the cosmic web without Dark Matter (whatever Dark Matter is) scientists cannot come up with a rival working theory to explain the universe at large, there was MOND (Modified Newtonian Dynamics) a few years ago but I have not heard any more about it recently.

 

[Flyaway]

Solar wind contributions to Earth’s oceans

Abstract
The isotopic composition of water in Earth’s oceans is challenging to recreate using a plausible mixture of known extraterrestrial sources such as asteroids—an additional isotopically light reservoir is required. The Sun’s solar wind could provide an answer to balance Earth’s water budget. We used atom probe tomography to directly observe an average ~1 mol% enrichment in water and hydroxyls in the solar-wind-irradiated rim of an olivine grain from the S-type asteroid Itokawa. We also experimentally confirm that H+ irradiation of silicate mineral surfaces produces water molecules. These results suggest that the Itokawa regolith could contain ~20 l m−3 of solar-wind-derived water and that such water reservoirs are probably ubiquitous on airless worlds throughout our Galaxy. The production of this isotopically light water reservoir by solar wind implantation into fine-grained silicates may have been a particularly important process in the early Solar System, potentially providing a means to recreate Earth’s current water isotope ratios.

Solar wind contributions to Earth’s oceans - Nature Astronomy

Water and hydroxyl enrichment in the solar-wind-irradiated rim of an olivine grain from asteroid Itokawa suggests that its regolith could contain ~20 l m−3 of water from solar wind—a potential water source for airless planetary bodies.

www.nature.com

Curtin graduate Dr. Luke Daly, now of the University of Glasgow, said the research not only gives scientists a remarkable insight into the past source of Earth's water, but could also help future space missions.

"How astronauts would get sufficient water, without carrying supplies, is one of the barriers of future space exploration," Dr. Daly said.

"Our research shows that the same space weathering process which created water on Itokawa likely occurred on other airless planets, meaning astronauts may be able to process fresh supplies of water straight from the dust on a planet's surface, such as the Moon."

Study suggests Sun is likely an unaccounted source of the Earth's water

Curtin University researchers have helped unravel the enduring mystery of the origins of the Earth's water, finding the Sun to be a surprising likely source.

phys.org

 

[Rhinocrates]

Solar wind contributions to Earth’s oceans

Study suggests Sun is likely an unaccounted source of the Earth's water

Curtin University researchers have helped unravel the enduring mystery of the origins of the Earth's water, finding the Sun to be a surprising likely source.

phys.org

Beat me to it again. Interesting in light of the study suggesting that TRAPPIST-1 planets didn't have a lengthy bombardment and hence might be dry.

It seems that every alternate week there are studies released saying that planets around red dwarfs can't be habitable or can be habitable.

I propose a law applicable to all sciences: for every ten studies there are nine equal and opposite studies. You just have to wait it out to find a consensus (and some direct observations).

 

[Flyaway]

Supermassive Black Holes on a Collision Course (ESOcast 246 Light)

View: https://youtu.be/GfNQfUloEyA

Using the ESO’s Very Large Telescope, astronomers have revealed the closest pair of supermassive black holes to Earth ever observed. This video summarises the discovery.

 

[Flyaway]

NASA’s Laser Communications Relay Demonstration (LCRD) moved one step closer to launch on Monday, Nov. 22, after a team of engineers fastened the payload fairing containing its host satellite to a United Launch Alliance (ULA) Atlas V 551 rocket. Launch is now targeted for Dec. 5, 2021, due to inclement weather during launch vehicle processing.

Lift and Mate Operations Complete for Space Test Program 3, Now Targeted for Dec. 5 – Kennedy Space Center

blogs.nasa.gov

 

[jeffb]

Dwarf planet Ceres may be home to an underground ocean

New analysis of data from the Dawn spacecraft suggests there may be a liquid water ocean beneath the Occator crater on Ceres, the largest asteroid in the solar system

www.newscientist.com

 

[Justo Miranda]

I would like to know if anyone has calculated the statistical chances that a probe can pass through the Oort Cloud without colliding with something. Is the density of objects within the cloud assumed to be uniform in all directions of the sphere? Any opinion?

 

[Flyaway]

NASA’s Next-Generation Asteroid Impact Monitoring System Goes Online

The new system improves the capabilities of NASA JPL’s Center for Near Earth Object Studies to assess the impact risk of asteroids that can come close to our planet.

To date, nearly 28,000 near-Earth asteroids (NEAs) have been found by survey telescopes that continually scan the night sky, adding new discoveries at a rate of about 3,000 per year. But as larger and more advanced survey telescopes turbocharge the search over the next few years, a rapid uptick in discoveries is expected. In anticipation of this increase, NASA astronomers have developed a next-generation impact monitoring algorithm called Sentry-II to better evaluate NEA impact probabilities.

Popular culture often depicts asteroids as chaotic objects that zoom haphazardly around our solar system, changing course unpredictably and threatening our planet without a moment’s notice. This is not the reality. Asteroids are extremely predictable celestial bodies that obey the laws of physics and follow knowable orbital paths around the Sun.

But sometimes, those paths can come very close to Earth’s future position and, because of small uncertainties in the asteroids’ positions, a future Earth impact cannot be completely ruled out. So, astronomers use sophisticated impact monitoring software to automatically calculate the impact risk.

Managed by NASA’s Jet Propulsion Laboratory in Southern California, the Center for Near Earth Object Studies (CNEOS) calculates every known NEA orbit to improve impact hazard assessments in support of NASA’s Planetary Defense Coordination Office (PDCO). CNEOS has monitored the impact risk posed by NEAs with software called Sentry, developed by JPL in 2002.

“The first version of Sentry was a very capable system that was in operation for almost 20 years,” said Javier Roa Vicens, who led the development of Sentry-II while working at JPL as a navigation engineer and recently moved to SpaceX. “It was based on some very smart mathematics: In under an hour, you could reliably get the impact probability for a newly discovered asteroid over the next 100 years – an incredible feat.”

But with Sentry-II, NASA has a tool that can rapidly calculate impact probabilities for all known NEAs, including some special cases not captured by the original Sentry. Sentry-II reports the objects of most risk in the CNEOS Sentry Table.

By systematically calculating impact probabilities in this new way, the researchers have made the impact monitoring system more robust, enabling NASA to confidently assess all potential impacts with odds as low as a few chances in 10 million.

Special Cases

As an asteroid travels through the solar system, the Sun’s gravitational pull dictates the path of its orbit, and the gravity of the planets will also tug at its trajectory in predictable ways. Sentry modeled to a high precision how these gravitational forces shaped an asteroid’s orbit, helping to predict where it will be far into the future. But it couldn’t account for non-gravitational forces, the most significant being the thermal forces caused by the Sun’s heat.

As an asteroid spins, sunlight heats the object’s dayside. The heated surface will then rotate to the asteroid’s shaded nightside and cool down. Infrared energy is released as it cools, generating a tiny yet continual thrust on the asteroid. This phenomenon is known as the Yarkovsky effect, which has little influence on the asteroid’s motion over short periods but can significantly change its path over decades and centuries.

View: https://youtu.be/Cb9IL8AqrGA


This video explains how asteroid Bennu’s orbit around the Sun was determined by considering gravitational and non-gravitational forces, helping scientists understand how the asteroid’s trajectory will change over time.
Credits: NASA’s Goddard Space Flight Center
“The fact that Sentry couldn’t automatically handle the Yarkovsky effect was a limitation,” said Davide Farnocchia, a navigation engineer at JPL who also helped develop Sentry-II. “Every time we came across a special case – like asteroids Apophis, Bennu, or 1950 DA – we had to do complex and time-consuming manual analyses. With Sentry-II, we don’t have to do that anymore.”

Another issue with the original Sentry algorithm was that it sometimes couldn’t accurately predict the impact probability of asteroids that undergo extremely close encounters with Earth. The motion of these NEAs gets significantly deflected by our planet’s gravity, and the post-encounter orbital uncertainties can grow dramatically. In those cases, the old Sentry’s calculations could fail, requiring manual intervention. Sentry-II doesn’t have that limitation.

“In terms of numbers, the special cases we’d find were a very tiny fraction of all the NEAs that we’d calculate impact probabilities for,” said Roa Vicens. “But we are going to discover many more of these special cases when NASA’s planned NEO Surveyor mission and the Vera C. Rubin Observatory in Chile go online, so we need to be prepared.”

Many Needles, One Haystack

This is how impact probabilities are calculated: When telescopes track a new NEA, astronomers measure the asteroid’s observed positions in the sky and report them to the Minor Planet Center. CNEOS then uses that data to determine the asteroid’s most likely orbit around the Sun. But because there are slight uncertainties in the asteroid’s observed position, its “most likely orbit” might not represent its true orbit. The true orbit is somewhere inside an uncertainty region, like a cloud of possibilities surrounding the most likely orbit.

To assess whether an impact is possible and narrow down where the true orbit may be, the original Sentry would make some assumptions as to how the uncertainty region may evolve. It would then select a set of evenly spaced points along a line spanning the uncertainty region. Each point represented a slightly different possible current location of the asteroid.

Sentry would then wind the clock forward, watch those “virtual asteroids” orbit the Sun, and see if any came near Earth in the future. If so, further calculations would be required to “zoom in” to see whether any intermediate points might impact Earth, and if they did, estimate the impact probability.

View: https://youtu.be/t94moJHoL2w


This animation shows an example of how the uncertainties in a near-Earth asteroid’s orbit can evolve with time. After such an asteroid’s close encounter with Earth, the uncertainty region becomes larger, making the possibility of future impacts more challenging to assess.
Credits: NASA/JPL-Caltech
Sentry-II has a different philosophy. The new algorithm models thousands of random points not limited by any assumptions about how the uncertainty region may evolve; instead, it selects random points throughout the entire uncertainty region. Sentry-II’s algorithm then asks: What are the possible orbits within the entire region of uncertainty that could hit Earth?

This way, the orbital determination calculations aren’t shaped by predetermined assumptions about which portions of the uncertainty region might lead to a possible impact. This allows Sentry-II to zero in on more very low probability impact scenarios, some of which Sentry may have missed.

Farnocchia likens the process to searching for needles in a haystack: The needles are possible impact scenarios, and the haystack is the uncertainty region. The more the uncertainty in an asteroid’s position, the bigger the haystack. Sentry would randomly poke at the haystack thousands of times looking for needles located near a single line stretching through the haystack. The assumption was that following this line was the best way of searching for needles. But Sentry-II assumes no line and instead throws thousands of tiny magnets randomly all over that haystack, which quickly get attracted to, and then find, the nearby needles.

“Sentry-II is a fantastic advancement in finding tiny impact probabilities for a huge range of scenarios,” said Steve Chesley, senior research scientist at JPL, who led the development of Sentry and collaborated on Sentry-II. “When the consequences of a future asteroid impact are so big, it pays to find even the smallest impact risk hiding in the data.”

A study describing Sentry-II was published in the Astronomical Journal on Dec. 1, 2021.

More information about CNEOS, asteroids, and near-Earth objects can be found at:

Center for NEO Studies

NASA's Near-Earth Object (NEO) web-site. Data related to Earth impact risk, close-approaches, and much more.

cneos.jpl.nasa.gov

For more information about PDCO, visit:

Planetary Defense at NASA - NASA Science

www.nasa.gov

 

[Hobbes]

I would like to know if anyone has calculated the statistical chances that a probe can pass through the Oort Cloud without colliding with something. Is the density of objects within the cloud assumed to be uniform in all directions of the sphere? Any opinion?

Verly little is known about the Oort cloud, There are some theories that predict density waves.
Going by wikipedia data: volume is 10^38 km^3, containing 5 Earth masses (10^25 kg) so 10^-8 g/m3. That's barely more populated than interstellar space. Chances of hitting something on the order of 10^-9.

 

[Justo Miranda]

I would like to know if anyone has calculated the statistical chances that a probe can pass through the Oort Cloud without colliding with something. Is the density of objects within the cloud assumed to be uniform in all directions of the sphere? Any opinion?

Verly little is known about the Oort cloud, There are some theories that predict density waves.
Going by wikipedia data: volume is 10^38 km^3, containing 5 Earth masses (10^25 kg) so 10^-8 g/m3. That's barely more populated than interstellar space. Chances of hitting something on the order of 10^-9.

Thanks.

 

[Flyaway]

Surprise planet found around extreme star pair (ESOcast 247 Light):

View: https://youtu.be/JuOz9QY6mjI