Planetary and Solar System Characteristics

Category: Planetary and Solar System Characteristics (page 2 of 4)

Asteroid Remains Around Dead Stars Reveal the Likely Fate of Our Solar System

Artist concept of an asteroid breaking up. (NASA/JPL-Caltech)

June 30th has been designated “Asteroid Day” to promote awareness of these small members of our solar system. But while asteroids are often discussed in the context of the risk they might pose to the Earth, their chewed up remains around other stars may also reveal the fate of our solar system.

It is 6.5 billion years into our future. The sun has fused hydrogen into a core of heavier helium. Compressed by its own gravity, the helium core releases heat and the sun begins to swell. It is the end of our star’s life, but what will happen to the solar system?

While very massive stars end their element-fusing days in a colossal explosion known as a supernovae, the majority of stars in our galaxy will take a less dramatic exit.

Our sun’s helium core will fuse to form carbon but there is not enough mass to achieve the crushing compression needed for the creation of heavier elements. Instead, the outer layers of the dying star will be blown away to leave a dense remnant with half the mass of our current sun, but squeezed down to the size of the Earth. This is a white dwarf; the most common of all stellar ends.

The life cycle of our sun

The white dwarf rapidly cools to become a dim twinkle in the sky. Within a few million years, our white dwarf will be less luminous that the sun today. Within 100 million years, it will be dimmer by a factor of 100. But examination of white dwarfs in our galaxy reveals this gentle dimming of the lights is not as peaceful as first appears.

The remnants of stars too light to fuse carbon, white dwarfs have atmospheres that should be thin shells of residue hydrogen and helium. Instead, observations have detected 20 different heavy elements in this envelope of gases that include rock-forming elements such as silicon and iron and volatiles such as carbon and nitrogen.

Infrared observations of over forty white dwarfs have additionally revealed compact dusty discs circling the dead stars. Sitting within the radius of a regular star, these could not have formed before the star shrank into a white dwarf. These must be the remains of what occurred as the star morphed from a regular fusion burner into a white dwarf.

This grizzly tale begins with the star’s expansion.… Read more

Know Thy Star, Know Thy Planet: How Gaia is Helping Nail Down Planet Sizes

May 18, 2018 / Elizabeth Tasker / 0 Comments

Gaia’s all-sky view of our Milky Way and neighboring galaxies. (ESA/Gaia/DPAC)

Last month, the European Space Agency’s Gaia missio n released the most accurate catalogue to date of positions and motions for a staggering 1.3 billion stars.

Let’s do a few comparisons so we can be suitably amazed. The total number of stars you can see without a telescope is less than 10,000. This includes visible stars in both the northern and southern hemispheres, so looking up on a very dark night will allow you to count only about half this number.

The data just released from Gaia is accurate to 0.04 milli-arcseconds. This is a measurement of the angle on the sky, and corresponds to the width of a human hair at a distance of over 300 miles (500 km.) These results are from 22 months of observations and Gaia will ultimately whittle down the stellar positions to within 0.025 milli-arcseconds, the width of a human hair at nearly 680 miles (1000 km.)

OK, so we are now impressed. But why is knowing the precise location of stars exciting to planet hunters?

The reason is that when we claim to measure the radius or mass of a planet, we are almost always measuring the relative size compared to the star. This is true for all planets discovered via the radial velocity and transit techniques — the most common exoplanet detection methods that account for over 95% of planet discoveries.

It means that if we underestimate the star size, our true planet size may balloon from being a close match to the Earth to a giant the size of Jupiter. If this is true for many observed planets, then all our formation and evolution theories will be a mess.

The size of a star is estimated from its brightness. Brightness depends on distance, as a small, close star can appear as bright as a distant giant. Errors in the precise location of stars therefore make a big mess of exoplanet data.

An artist’s impression of the Gaia spacecraft — which is on a mission to chart a three-dimensional map of our Milky Way. In the process it will expand our understanding of the composition, formation and evolution of the galaxy. (ESA/D. Ducros)

This issue has been playing on the minds of exoplanet hunters.

In 2014, a journal paper authored by Fabienne Bastien from Vanderbilt University suggested that nearly half of the brightest stars observed by the Kepler Space Telescope are not regular stars like our sun, but actually are distant and much larger sub-giant stars.… Read more

Exoplanet Fomalhaut b On the Move

April 30, 2018 / Marc Kaufman / 0 Comments

Enlarge and enjoy. Fomalhaut b on its very long (1,700 year) and elliptica orbit, as seen here in five images taken by the Hubble Space Telescope over seven years. The reference to “20 au” means that the bar shows a distance of 20 astronomical units, or 20 times the distance from the sun to the Earth. (Jason Wang/Paul Kalas; UC Berkeley)

Direct imaging of exoplanets remains in its infancy, but goodness what a treat it is already and what a promise of things to come.

Almost all of the 3,714 exoplanets confirmed so far were detected via the powerful but indirect transit and radial velocity methods — measures of slightly decreased light as a planet crosses in front of its star, or the measured wobble of a star caused by the gravitational pull of a planet.

But now 44 planets have also been detected by telescopes — in space and on the ground — looking directly at distant stars. Using increasingly sophisticated coronagraphs to block out the blinding light of the stars, these tiny and often difficult-to-identify specks are nonetheless results that are precious to scientists and the public.

To me, they make exoplanet science accessible as perhaps nothing else so far. Additionally, they strike me as moving — and I don’t mean in orbit. Rather, as when you see your own insides via x-rays or MRIs, direct imaging of exoplanets provides a glimpse into the otherwise hidden realities of our world.

And in the years ahead – actually, most likely the decades ahead — this kind of direct imaging of our astronomical neighborhood will become increasingly powerful and common.

This is how the astronomers studying the Fomalhaut system describe what you are seeing:

“The Fomalhaut system harbors a large ring of rocky debris that is analogous to our Kuiper belt. Inside this ring, the planet Fomalhaut b is on a trajectory that will send it far beyond the ring in a highly elliptical orbit.

“The nature of the planet remains mysterious, with the leading theory being the planet is surrounded by its own ring or a sphere of dust.”

A simulation of one possible orbit for Fomalhaut b derived from the analysis of Hubble Space Telescope data between 2004 and 2012, presented in January 2013 by astronomers Paul Kalas and James Graham of Berkeley, Michael Fitzgerald of UCLA and Mark Clampin of NASA/Goddard. (Paul Kalas)

Fomalhaut b was first described in 2008 by Paul Kalas, James Graham and colleagues at the University of California, Berkeley. … Read more

The Just-Approved European ARIEL Mission Will Be First Dedicated to Probing Exoplanet Atmospheres

March 29, 2018 / Elizabeth Tasker / 0 Comments

The Ariel space telescope will explore the atmospheres of exoplanets. (Artist impression, ESA)

The European Space Agency (ESA) has approved the ARIEL space mission—the world’s first dedicated exoplanet atmosphere sniffer— to fly in 2028.

ARIEL stands for the “Atmospheric Remote-sensing Infrared Exoplanet Large-Survey mission.” It is a space telescope that can detect which atoms and molecules are present in the atmosphere of an exoplanet.

The mission was selected as a medium class mission in the ESA Cosmic Vision program; the agency’s decadal plan for space missions that spans 2015 – 2025.

One of the central themes for Cosmic Vision is uncovering the conditions for planet formation and the origins of life. This has resulted in three dedicated exoplanet missions within the same decadal plan. ARIEL will join CHEOPS (in the small class mission category) and PLATO (another medium class mission) in studying worlds beyond our own sun.

Yet ARIEL is a different type of telescope from the other exoplanet-focused missions. To understand why, we need to examine what properties we can observe of these distance exo-worlds.

Exoplanet missions can be broadly divided into two types. The first type are the exoplanet hunter missions that search the skies for new worlds.

These are spacecraft and instruments such as the NASA Kepler Space Telescope. Since it launched in 2009, Kepler has been an incredibly prolific planet hunter. The telescope has found thousands of planets, modeled their orbits and told us about the distribution of their sizes.

From Kepler, we have learnt that planet formation is common, that it can occur around stars far different from our own sun, and that these worlds can have a vast range of sizes and myriad of orbits quite unlike our own Solar System.

Current and future (or proposed) space missions with capacities to identify and characterize exoplanets. The very productive CoRotT mission is, however, missing. It searched for and found many exoplanets from 2006 to 2013. (NASA,ESA: T. Wynne/JPL, composited by Barbara Aulicino)

However, the information Kepler is able to provide about individual planets is very limited. The telescope monitors stars for the tiny drop in light as the planet crosses (or “transits”) the star’s surface. From this, astronomers can measure the radius of the planet and its orbital period but nothing about the planet’s surface conditions.

The result is a little like knowing the number of students and distribution of grades in a particular school, but having no idea if the student who sits in the third row actually likes math.… Read more

The Northern Lights (Part Two)

March 5, 2018 / Marc Kaufman / 0 Comments

Northern Lights at a latitude of about 70 degrees north, well within the Arctic Circle. These photos were taken about 30 miles from the town of Alta. (Lisa Braithwaite)

In my recent column about The Northern Lights, the Magnetic Field and Life, I explored the science and the beauty of our planet’s aurora borealis, one of the great natural phenomenon we are most fortunate to see in the far North (and much less frequently in the not-quite-so-far North.)

I learned the hard way that an IPhone camera was really not up to the job; indeed, the battery froze soon after leaving my pocket in the 10 degrees F cold. So the column had few images from where I actually was — about a half hour outside of the Arctic Circle town of Alta.

But here now are some images taken by a generous visitor to the same faraway lodge, who was present the same time as myself.

Her name is Lisa Braithwaite and she is an avid amateur photographer and marketing manager for two popular sites in the English Lake District. This was her first hunting trip for the Northern Lights, and she got lucky. Even in the far northern Norway winter the lights come and go unpredictably — though you can increase your chances if you show up during a time when the sun is actively sending out solar flares.

She came with a Panasonic Lumix DMC-G5 camera and did a lot of research beforehand to increase her chances of capturing the drama should the lights appear. Her ISOs ranged from 1,600 to 64,000, and her shutter speed from 5 to 15 seconds. The aperture setting was 3.5.

In addition to showing some of her work, further on I describe a new NASA-led and international program, based in Norway, to study the still incompletely understood dynamics of what happens when very high energy particles from solar flares meet Earth’s atmosphere.

Partnering with the Japanese Aerospace Exploration Agency (JAXA,) the University of Oslo an other American universities, the two year project will send eleven rockets filled with instruments into the ionosphere to study phenomenon such as the auroral winds and the turbulence that can cause so much trouble to communications networks.

But first, here are some morre of Braithwaite’s images, most taken over a one hour period on a single night.

Arcs are a common feature of the lights, sometimes reaching across the sky.

Putting Together a Community Strategy To Search for Extraterrestrial Life

January 15, 2018 / Marc Kaufman / 0 Comments

I regret that the formatting of this column was askew earlier; I hope it didn’t make reading too difficult. But now those problems are fixed.

The scientific search underway for life beyond Earth requires input from many disciplines and fields. Strategies forward have to hear and take in what scientists in those many fields have to say. (NASA)

Behind the front page space science discoveries that tell us about the intricacies and wonders of our world are generally years of technical and intellectual development, years of planning and refining, years of problem-defining and problem-solving. And before all this, there also years of brainstorming, analysis and strategizing about which science goals should have the highest priorities and which might be most attainable.

That latter process is underway now in regarding the search for life in the solar system and beyond, with numerous teams of scientists tackling specific areas of interest and concern and turning their group discussions into white papers. In this case, the white papers will then go on to the National Academy of Sciences for a blue-ribbon panel review and ultimately recommendations on which subjects are exciting and mature enough for inclusion in a decadal survey and possible funding.

This is a generally little-known part of the process that results in discoveries, but scientists certainly understand how they are essential. That’s why hundreds of scientists contribute their ideas and time — often unpaid — to help put together these foundational documents.

With its call for extraterrestrial habitability white papers, the NAS got more than 20 diverse and often deeply thought out offerings. The papers will be studied now by an ad hoc, blue ribbon committee of scientists selected by the NAS, which will have the first of two public meetings in Irvine, Calif. on Jan. 16-18.

Shawn Domagal-Goldman, a leader of many NASA study projects and a astrobiologist at NASA’s Goddard Space Fight Center. (NASA)

Then their recommendations go up further to the decadal survey teams that will set formal NASA priorities for the field of astronomy and astrophysics and planetary science. This community-based process that has worked well for many scientific disciplines since they began in the late 1950s.

I’m particularly familiar with two of these white paper processes — one produced at the Earth-Life Science Institute (ELSI) in Tokyo and the other with NASA’s Nexus for Exoplanet System Science (NExSS.) What they have to say is most interesting.… Read more

Two Tempting Reprise Missions: Explore Titan or Bring Back a Piece of A Comet

December 22, 2017 / Marc Kaufman / 0 Comments

Dragonfly is a quadcopter lander that would take advantage of the environment on Titan to fly to multiple locations, some hundreds of miles apart, to sample materials and determine the composition of the surface. A central goal would be to analyze Titan’s organic chemistry and assess its habitability. (NASA)

Unmanned missions to planets and moons and asteroids in our solar system have been some of NASA’s most successful efforts in recent years, with completed or on-going ventures to Mars, Saturn, Jupiter, the asteroid Bennu, our moon, Pluto, Mercury and bodies around them all. On deck are a funded mission to Europa, another to Mars and one to the unique metal asteroid 16 Psyche orbiting the sun between Mars and Jupiter.

We are now closer to adding another New Frontiers class destination to that list, and NASA announced this week that it will be to either Saturn’s moon Titan or to the comet 67P/Churyumov-Gerasimenko.

After assessing 12 possible New Frontiers proposals, these two made the cut and will receive $4 million each to further advance their proposed science and technology. One of them will be selected in spring of 2019 for launch in the mid 2020s.

With the announcement, associate administrator for NASA’s Science Mission Directorate Thomas Zurbuchen described the upcoming choice as between two “tantalizing investigations that seek to answer some of the biggest questions in our solar system today.”

Those questions would be: How did water and other compounds essential for life arrive on Earth? Comets carry ancient samples of both, and so can potentially provide answers.

And with its large inventories of nitrogen, methane and other organic compounds, is Titan potentially habitable? Then there’s the added and very intriguing prospect of visiting the methane lakes of that frigid moon.

The CAESAR mission would return to the nucleus of comet explored by the European Space Agency’s Rosetta mission, and its lander Philae. (NASA)

Both destinations selected have actually been visited before.

The European Space Agency’s Rosetta mission orbited the comet 67P/Churyumov-Gerasimenko comet for two years and deployed a lander, which did touch down but sent back data for only intermittently for several days.

And the NASA’s Cassini-Huygens mission to Saturn passed by Titan regularly during its decade exploring that system, and the ESA’s Huygens probe did land on Titan and sent back information for a short time.

So both Rosetta and Cassini-Huygens began the process of understanding these distant and potentially revelatory destinations, and now NASA is looking to take it further.… Read more

Can You Overwater a Planet?

November 22, 2017 / Elizabeth Tasker / 0 Comments

Water worlds, especially if they have no land on them, are unlikely to be home to life, or at least life we can detect. Some of the basic atmospheric and mineral cycles that make a planet habitable will be absent. Cool animation of such a world. (NASA)

Wherever we find water on Earth, we find life. It is a connection that extends to the most inhospitable locations, such as the acidic pools of Yellowstone, the black smokers on the ocean floor or the cracks in frozen glaciers. This intimate relationship led to the NASA maxim, “Follow the Water”, when searching for life on other planets.

Yet it turns out you can have too much of a good thing. In the November NExSS Habitable Worlds workshop in Wyoming, researchers discussed what would happen if you over-watered a planet. The conclusions were grim.

Despite oceans covering over 70% of our planet’s surface, the Earth is relatively water-poor, with water only making up approximately 0.1% of the Earth’s mass. This deficit is due to our location in the Solar System, which was too warm to incorporate frozen ices into the forming Earth. Instead, it is widely — though not exclusively — theorized that the Earth formed dry and water was later delivered by impacts from icy meteorites. It is a theory that two asteroid missions, NASA’s OSIRIS-REx and JAXA’s Hayabusa2, will test when they reach their destinations next year.

But not all planets orbit where they were formed. Around other stars, planets frequently show evidence of having migrated to their present orbit from a birth location elsewhere in the planetary system.

One example are the seven planets orbiting the star, TRAPPIST-1. Discovered in February this year, these Earth-sized worlds orbit in resonance, meaning that their orbital times are nearly exact integer ratios. Such a pattern is thought to occur in systems of planets that formed further away from the star and migrated inwards.

Trappist-1 and some of its seven orbiting planets. They would have been sterilized by high levels of radiation in the early eons of that solar system — unless they were formed far out and then migrated in. That scenario would also allow for the planets to contain substantial amounts of water. (NASA)

The TRAPPIST-1 worlds currently orbit in a temperate region where the levels of radiation from the star are similar to that received by our terrestrial worlds.… Read more

Cassini Inside the Rings of Saturn

August 29, 2017 / Marc Kaufman / 0 Comments

Movie produced from images taken while Cassini flew inside the rings of Saturn – a first. (NASA/JPL-Caltech/Space Science Institute)

The triumphant Cassini mission to Saturn will be coming to an end on September 15, when the spacecraft dives into the planet. Running out of fuel, NASA chose to end the mission that way rather than run the risk of having the vehicle wander and ultimately land on Europa or Enceladus, potentially contaminating two moons very high on the list of possible habitable locales in our solar system.

Both the science and the images coming back from this descent are (and will be) pioneering, as they bring to an end one of the most successful and revelatory missions in NASA history.

As NASA promised, the 22-dive descent has already produced some of the most compelling images of Saturn and its rings. Most especially, Cassini has delivered the remarkable 21-image video above. The images were taken over a four minutes period on August 20 using a wide-angle camera.

The spacecraft captured the images from within the gap between the planet and its rings, looking outward as the spacecraft made one of its final dives through the ring-planet gap as part of the finale.

The entirety of the main rings can be seen here, but due to the low viewing angle, the rings appear extremely foreshortened. The perspective shifts from the sunlit side of the rings to the unlit side, where sunlight filters through.

On the sunlit side, the grayish C ring looks larger in the foreground because it is closer; beyond it is the bright B ring and slightly less-bright A ring, with the Cassini Division between them. The F ring is also fairly easy to make out.

NASA’s Cassini spacecraft will make 22 orbits of Saturn during its Grand Finale, exploring a totally new region between the planet and its rings. NASA/JPL-Caltech

While the Cassini team has to keep clear of the rings, the spacecraft is expected to get close enough to most likely answer one of the most long-debated questions about Saturn: how old are those grand features, unique in our solar system?

One school of thought says they date from the earliest formation of the planet, some 4.6 billion years ago. In other words, they’ve been there as long as the planet has been there.

But another school says they are a potentially much newer addition. They could potentially be the result of the break-up of a moon (of which Saturn has 53-plus) or a comet, or perhaps of several moons at different times.… Read more

Phobos and Deimos: Captured Asteroids or Cut From Ancient Mars?

June 16, 2017 / Elizabeth Tasker / 0 Comments

Illustration of Mars with its two moons, Phobos and Deimos. (NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ.)

The global success rate for sending missions to land on the moons of Mars has hardly been impressive — coming in at zero out of three attempts. They were all led by the Russian (or former Soviet) space agencies, in collaboration with organizations ranging from the Chinese and Bulgarian space agencies to the Paris Observatory and the U.S. Planetary Society.

Now the Japanese space agency JAXA has approved its own mission to Phobos and Deimos, scheduled to launch from the Tanegashima Space Center in September 2024.

The Martian Moons eXploration (MMX) spacecraft will arrive at Mars in August 2025 and spend the next three years exploring the two moons and the environment around Mars. During this time, the spacecraft will drop to the surface of one of the moons and collect a sample to bring back to Earth. Probe and sample are scheduled to return to Earth in the summer of 2029.

Mars takes its name from the god of war in ancient Greek and Roman mythology. The Greek god Ares became Mars in the Roman adaptation of the deities. Mars’s two moons are named for Phobos and Deimos; in legend the twin sons of Ares who personified fear and panic.

Today, what the moons together personify is a compelling mystery, one regarding how in reality they came to be.

Both Martian moons are small, with Phobos’s average diameter measuring 22.2km, while the even smaller Deimos has an average size of just 13km. This makes even Phobos’s surface area only comparable to that of Tokyo. Their diminutive proportions means that the moons resemble asteroids, with irregular structures due to their gravity being too weak to pull them into spheres.

This leads to the question that has inspired a long-running debate: Were Phobos and Deimos formed during an impact with Mars, or are they asteroids that have been captured by Mars’s gravity?

Phobos and Deimos, photographed by the Mars Reconnaissance Orbiter. (NASA/JPL)

Our own Moon is thought to have been created when a Mars-sized body slammed into the early Earth. Debris from the collision was thrown into the Earth’s orbit where is coalesced into our only natural satellite.

A similar scenario is possible for Phobos and Deimos. In the late stages of our solar system’s formation, giant impacts such as the one that struck the Earth were relatively common.… Read more

Many Worlds