Should We Call Pluto a Planet?

Astronomers once called Pluto the ninth planet. In 2006, the International Astronomical Union, IAU, downgraded Pluto to the status of dwarf planet. After the New Horizons craft flew by Pluto in 2015, it showed us a very dynamic world. Many astronomers and a large percentage of the public now believe we should reconsider Pluto’s demotion.

Pluto as seen by the New Horizons spacecraft. 

Since before written history, humans have known of seven regularly observed heavenly bodies that didn’t behave like the vast majority of stars. They called them planets, Greek for “wanderer.” In those ancient times, they considered anything that changed its position relative to the “fixed stars” to be a planet. Since both the sun and the Moon moved relative to the fixed stars, they were also considered planets until Copernicus proved that planets circled the sun and the Moon circled Earth.

Astronomers then recognized six planets, Mercury, Venus, Earth, Mars, Jupiter, and Saturn. Comets also orbited the sun, but because they had weird orbits and grew a tail, they were considered different types of celestial objects. That changed in 1781 when William Herschel discovered Uranus and Italian astronomer Giuseppe Piazzi discovered Ceres in 1801 between Mars and Jupiter while searching for comets. Both orbited the sun.

Ceres, the largest member of the Asteroid Belt.

Initially, astronomers called Ceres the smallest planet until many more such objects were discovered in the same area of our solar system. They reclassified Ceres and all those other even smaller objects as “asteroids,” calling that region the Asteroid Belt.

In 1846, two astronomers independently discovered Neptune, adding an 8^th planet to the solar system. Clyde Tombaugh added Pluto in 1930, making nine planets, and there it stayed for years.

In the 1990s, astronomers began finding many more objects beyond Neptune. They were small like Pluto and in the area of our solar system that was relatively crowded, unlike the inner parts. Some astronomers feared that it might be time to get a more scientifically based definition of “planet.”  

At the 2006 IAU meeting, astronomers agreed to redefine what constitutes a planet. There were two camps: geophysicists and dynamists. They all agreed that it had to orbit a star. Geophysicists said that any object big enough that its gravity pulled it into a spherical or nearly spherical shape should be a planet. Dynamists argued that a planet must also be large enough to “clear its orbital area of debris.” Ceres couldn’t be a planet since, even though it is round, there were many asteroids in the same region. Likewise, round Pluto shared its region with many thousands of objects.

The dynamists won. Pluto, Ceres, and other round solar system bodies became dwarf planets. Along with those two, astronomers now recognize three others, Haumea, Makemake, and Eris, all beyond Neptune, as dwarf planets. There may be many more that we just don’t have enough data on yet.

Count me in the camp of the geophysicists. If it’s big enough to pull itself into a nearly circular shape, technically called hydrostatic equilibrium, then I believe it should be a planet. I’m convinced that the dynamists just didn’t want to remember that many planet names.

  

    Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After publishing it there, I post that same column to my blog page.

   This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

Did Earth Once Possess a Ring Like Saturn?

 When I show people astronomical sights through my telescope, the one view that elicits the most comments is Saturn with its rings. Many times I’ve heard people say “Wow! That’s amazing.” Or, “Oh, that’s not real. You have a picture in there.” Saturn, more than any other common backyard telescope target, looks like the pictures you’ve seen in books.

Saturn.

Saturn isn’t the only planet with a ring system. Jupiter, Uranus, and Neptune also have rings but are only visible with very powerful telescopes or spacecraft passing nearby.

Imagine the sense of awe if we lived on a planet with rings, something we sometimes see in science fiction movies. Had you been around on Earth 466 million years ago, you might have been able to enjoy that very experience. A recent study suggests that Earth may very well have sported a ring like Saturn.

Artist's conception of Earth with rings.

Planetary rings are ephemeral. They don’t last forever, although they do exist for millions of years. The evidence for Earth’s possible ring is circumstantial but quite intriguing. Starting about 466 million years ago, Earth experienced a period of enhanced meteor cratering, a period known as the Ordovician impact spike. During that cratering period, virtually all of the impacts on Earth, centered on a narrow band along the equator. Typically, impacts should occur randomly over the Earth’s surface.

This narrow cratering band implies that the objects striking Earth all came from that area of the sky over the equator. The easiest explanation for such a narrow band of cratering events along the equator is a ring of debris encircling our planet. If a ring forms around a planet, it will always settle over the equator.

During the same time frame, sedimentary rocks show a large increase in L chondrite material. L chondrite-type asteroids are common in the asteroid belt. Denizens in the asteroid belt occasionally collide, scattering debris around the solar system. 

Artist's conception of two asteroids colliding. 

The researchers, led by Andrew G. Tomkins, a geologist at Monash University in Australia, suggest that one large fragment came close to Earth, passing so closely that Earth’s gravity shattered it and the debris formed a ring.

Based on the cratering record, the study participants claimed the ring lasted approximately 40 million years, a typical lifetime for a planetary ring. During that same period of time, Earth experienced one of its most intense glaciation events and mass extinctions known as the Hirnantian global icehouse period. The researchers suggest that shading from the ring decreased solar radiation reaching the planet’s surface, triggering the short but intense glaciation period. “The existence of such a ring, forming around 466 million years ago and persisting for a few tens of millions of years could explain several puzzles in our planet’s past,” Tomkins wrote.

None of this evidence is absolute proof that we once had a ring like Saturn’s, but it is strongly suggestive. More work needs to be done to help corroborate their conclusion.

 

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After publishing it there, I post that column on my blog page.

 This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

How the Moon May Save Our Plants and Animals

        As you start reading this article, you’ll likely wonder what this has to do with astronomy. But stay

 with me. Astronomy may play a pivotal role in helping solve this problem.

Species extinctions, both plant and animal, happen all the time. Scientists estimate that some 10% of species go extinct every 10 million years. One estimate claims that 99.999% of all species that have ever lived on Earth have gone extinct. But there are times in the vast history of life on Earth where species vanished at much higher rates, events known as mass extinctions. Scientists recognize five major mass extinctions. And some feel we are now at the beginning of a sixth one, this one caused primarily by human activity, like habitat destruction, overhunting, pollution, and global warming. Over the past few hundred years, extinctions climbed over 1000 times the background rate. 

To protect the world’s plant species, particularly those used for food, the Svalbard Global Seed Vault was established in 2008 to preserve global agricultural biodiversity. An international consortium chose a site on the Norwegian island of Spitsbergen. Ice, snow, and frozen tundra covered the island. This extreme cold would preserve the seeds stored there in case of an agricultural disaster.  It houses over one million varieties of seeds.

Svalbard Global Seed Fault

  In 2017, global warming caused heavy rain on the island instead of the normal snowfall. The vault flooded, although the water did not reach the seeds. This led to researchers brainstorming a way to protect the seeds against such disasters. And, other researchers wanted to also preserve animals in danger of extinction by securely storing DNA in cryogenic deep freeze. But, where could such a repository be constructed that wouldn’t be at the mercy of power loss, wars, or global warming?

Many scientists are now considering the Moon as the ideal location. At the Moon’s South Pole, astronomers have discovered numerous craters that exist in perpetual shadow. Sunlight never reaches the bottom of these craters. Since the Moon has no atmosphere to spread warmth from the sun, these permanently shadowed regions remain at around -196 degrees, the minimum needed to protect animal cells long-term.

Lunar craters near the South Pole that have permanently shadowed areas. Temperatures here never get above -195 degrees Fahrenheit.

 

This may seem like a wild idea, but as research scientist Mary Hagedorn, of the Smithsonian National Zoo and Conservation Biology Institute in Washington D.C. says, “It’s very good to have as many plans as possible, especially when it comes to saving our biodiversity and life on Earth.” 

Scientists have numerous satellites orbiting the Moon, and the data they send back just may help us save animals from extinction and important agricultural plants from natural or manmade disasters.

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After publishing it there, I post that same column on my blog page.

 This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

 

 

A Possible Signature of an Advanced Civilization

 As we humans grow in numbers and technological sophistication, we will need to generate more and more energy for our use. That likely means ever more reliance on renewable sources of energy like solar and wind energy. Even so, there will come a point when we have tapped all available energy sources our planet has.

We do, however, live quite close to an almost endless source of energy: our sun.

In 1960, physicist Freeman Dyson proposed that an advanced civilization might dismantle all the other planets, asteroids, and everything else in its solar system to create a sphere surrounding its star to collect all the solar energy it emits to run the civilization. Because of the 2^nd Law of Thermodynamics, such a Dyson Sphere would necessarily radiate excess heat in the form of a strong infrared glow. Dyson suggested that we could detect excess IR radiation from any such civilizations in our galaxy.

Illustration Dyson Sphere under construction 

Credit dottedhippo-iStock-Getty Images Plus

If a civilization is in the process of building a Dyson sphere around its star, we should detect periodic dimming of the star as the completed parts orbit it. Those dips in brightness would look different than a planet orbiting the star, of which we have discovered thousands. A Jupiter-like planet would block less than one percent of the star’s light.

In 2015, astronomer Tabetha “Tabby” Boyajian discovered a star that displayed light dips of up to 22 percent. Astronomers dubbed it Tabby’s Star. Initially, they thought that this star had hundreds of comets in a cluster that crossed in front of the star. However, observations ruled that out. Many armchair scientists, and even a few astronomers, suggested it might be an incomplete Dyson sphere. With more observations, most astronomers accepted that the most likely cause of the light variations is a large dust cloud, probably from a moon that had shattered, and parts of the dust cloud periodically blocked some of the star’s light.

The hallmarks of a Dyson sphere can be summed up easily: variability in a star’s brightness and an excess of IR radiation of a particular pattern due to waste heat. With Tabby’s star, the IR excess doesn’t exactly match a Dyson sphere. The cloud of dust fits it better.

Artist's conception of a partial Dyson Sphere around Tabby's Star

Recently, two separate studies looked at the data from 3 satellite missions that have examined millions of stars in the Milky Way looking for Dyson sphere candidates. One group led by PhD student Matías Suazo at Uppsala University in Sweden describes their study as “searching for extraterrestrial intelligence using indirect signatures of astroengineering,” in other words Dyson spheres. They came across more than a few compelling candidates. Fifty-three to be exact, stars that possessed both accepted signatures of Dyson spheres.

Neither group has yet convinced the astronomical community at large that they have indeed found Dyson spheres, but most agree the studies are intriguing and need further study.

In 1964, a Soviet astronomer Nikolai Kardashev proposed a method of measuring a civilization’s level of technological sophistication. He determined a civilization’s level by the energy sources it can utilize. According to the Kardashev Scale, a type I civilization can utilize and control all the energy sources of its home planet. That would include taming and using the energy of natural events such as volcanoes, tornadoes, earthquakes, etc.

A Type II civilization captures and uses all the available energy of its host star by creating a Dyson sphere. A Type III civilization captures all the energy emitted by its galaxy, every star, black hole, etc. Earth is currently considered to be a Type 0.7 civilization.

Have we finally found Type II civilizations? Only further study can answer that question.

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

 

 

The Amazing Hubble Telescope

 The Hubble Space Telescope has been and continues to be one of humanity’s greatest scientific instruments. With it, astronomers have already made 1.6 million observations and written more than 21,000 scientific papers. It added dramatically to our knowledge of the universe. Being such a complex instrument, NASA designed it so that it could be periodically serviced, replacing parts that wear out over time.  Five servicing missions visited Hubble. The most important was the very first one. It corrected a tiny mistake in the shape of its main mirror, which was off by less than the width of a human hair. The other four service missions replaced items such as batteries, gyroscopes, and electronic boxes, all of which have limited life. On some missions, astronauts installed state-of-the-art science instruments. Each service mission left Hubble a more capable and more productive observatory.

Hubble Space Telescope, credit STSCI, NASA, ESA

And capable it is. It showed us things astronomers never even guessed might be out there. Perhaps the most amazing science it produced came in the form of a series of long-exposure photographs, 342 in all, with a total exposure time of over 100 hours, known as the Hubble Deep Field. They pointed it to an apparently empty spot near the Big Dipper, a patch of sky about the equivalent of a pinhead at arm’s length.

Hubble Deep Field, credit NASA, ESA

Expecting to find maybe a few distant galaxies, the final combined images revealed more than 3,000 galaxies including what were at the time the most distant objects ever seen. The image amazed astronomers with the new data they obtained. That project was such a success that astronomers did another version from a spot in the southern hemisphere sky. With the success of those two images, astronomers then used Hubble to create the Ultra Deep Field image. It was a combination of 800 images taken over eleven and a half days, revealing more than 10,000 galaxies and again setting new distance records.

Hubble Ultra Deep Field, credit NASA, ESA

Hubble’s discoveries range far beyond simply observing thousands of galaxies in apparently empty patches of the sky. It was instrumental in discovering the existence and distribution of Dark Matter. The speed at which a planet orbits the sun depends on its distance from the sun, with planets farther out moving slower due to distance from the sun’s gravity. By the same token, stars at a galaxy’s edge should move slower than those closer in. But Hubble’s measurements showed that stars across the entire galaxy move at virtually the same speed, and move so fast that the gravity from all the matter of the galaxy couldn’t hold the galaxy together. Galaxies had to be embedded in a large shell of gravity-producing but invisible matter. Hubble was able to map the distribution of dark matter around the universe, helping to show it accounts for 85% of the matter in the universe. Using Albert Einstein's prediction that gravity can focus light, Hubble was used to take images of distant objects the light of which is focused by intervening sources of gravity. By studying these, they could measure the gravity from dark matter sources.

Gravitational Lensing from Dark Matter surrounding a galaxy cluster, credit Gravitational lensing, credit NASA, ESA, and J. Lotz

Hubble data measured the speed at which the universe expands, showing that the expansion is speeding up, leading to the discovery of Dark Energy. Hubble helped to verify the existence of exoplanets, those orbiting other stars. Astronomers used Hubble to study the formation and evolution of galaxies. Because of its keen vision, it helped astronomers better understand how stars change with age, the mechanics of supernovas, and the cause of short gamma-ray bursts, a subject that puzzled astronomers for many years. And this is only the tip of Hubble’s accomplishment iceberg.

We no longer have the space shuttle that flew astronauts on all the Hubble servicing missions. Now, it only has two functioning gyroscopes, which enable its precise pointing. Any observation it makes from now on will take more time. Hubble’s end is certainly in sight.

The Webb Space Telescope, Hubble’s successor, has taken the mantle as the best space telescope, but astronomers will still mourn Hubble’s passing whenever its mission finally ends.

 

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

Our Shrinking Moon

 You have probably heard that hot things expand and cold things contract. Maybe you learned that if a lid jar is stuck too tightly for you to open it, you can run hot water over the lid. The heat expands the metal lid, making it looser and therefore easier to open.

You may even experience this at night in your house. During the heating of the day, the wood in your house expands just a bit. In the cooler air of nighttime, the wood shrinks. You may hear this as creaks around your house. That’s not ghosts but rather the wooden parts rubbing together ever so slightly as the wood shrinks. My ghost-phunting team spends a lot of time explaining to homeowners who are convinced their home is haunted that those footsteps they hear are actually the thermal creaks of their house cooling and shrinking ever so slightly causing the wood two-by-fours to rub together. 

Jar lids and houses aren’t the only things that expand and contract when subjected to heat and cold. Any rigid solid object will react to temperature this way. Even rocks. The seasonal heating and cooling cycle is a contributing cause of the erosion of mountains. As the rock heats up in summer months, tiny cracks form that can become filled with moisture. During the cold winter, the water freezes. Water is one material that actually expands when it freezes as the water molecules rearrange into a crystalline pattern. As the ice expands, it widens the cracks, eventually causing bits of the rock to crumble into smaller bits.

Full Moon

Now think of a larger object, much larger, like our Moon. It formed about four and a half billion years ago when a Mars-sized object called Theia slammed into the newly formed Earth. Theia’s molten iron core sank to the center of our planet, joining our molten iron core. Geologists recently identified two large hunks of molten rock surrounding our planet’s core that they believe are remnants of the Theia.

Much of the rocky outer parts of Theia and some of Earth’s rocky surface parts were flung off in the collision and went into orbit around the now larger Earth. That debris eventually coalesced into the Moon. This new Moon slowly cooled and, as it did, it began shrinking. And that shrinking continues today.NASA satellites orbiting the Moon have photographed most of its surface. Planetary geologists have identified numerous scarps on the lunar surface, wrinkles caused by the Moon’s shrinkage. This is the same phenomenon that happens to an apple’s skin. It shrinks as it ages and dries out, causing it to wrinkle, just like our Moon’s surface.

                            An example of a lunar scarp.

Earth sits in the center of our sun’s habitable zone, the region where liquid water can exist on the surface of our planet. Venus orbits just inside the habitable zone. As a result, Earth is a lush planet full of life, while Venus is a hellish planet with surface temperatures hot enough to melt lead. But, if Venus orbited where Earth does, it likely would be a planet with life. It’s just a bit smaller than Earth and made of the same stuff as Earth. But for the specific orbital paths of the two planets, Venus would be a life-bearing planet.

On May 23^rd, NASA announced the discovery of a Venus-sized planet in the habitable zone of the star Gliese 12, only 40 light years away, virtually in our backyard as astronomical distances go. We have no idea if life developed there, but it is certainly a strong candidate for us to study further.

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

 This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

A Unique Sight? Every Night.

 Change is inevitable in our lives. We are born and grow older and taller. We might have children and we’ll watch them grow and change. Our hair eventually turns grey, or in my case, falls out. Our eyesight may fade, our joints may become stiffer.

 We grow older as does everyone we know and care about. Birth and death are a constant part of our world. Day turns into night; spring turns into summer. The clothes we wear at different times of the year, even the fashions we wear now as opposed to just a few years ago. But those changes are superficial.

 Would you like to see an absolutely unique sight? One you’ve never seen and one you’ll never see again? Wait until it gets dark, go outside, and look at the night sky. Do you see it? It has never been seen before, and never will again. It is tonight’s sky.

 The sky has never looked exactly as it does tonight and will never do so again.

 We think of the night sky as being constant. Oh, sure, the constellations move across the night sky from east to west, just like the sun in the daytime. The constellations visible in the night sky now will be almost completely different in six months. But, every April 15^th, we see the same stars. The sun will rise in a slightly different location tomorrow than it did today, but in one year, it will return to where it rose this morning.

 But the night sky changes in a way that all those seeming cycles never actually repeat. As the planets move in their annual dance around the sun, their pattern in the sky constantly changes. You’ll never see the exact arrangement of the planets again that you will see tonight.

 

The planets orbiting our sun.

Our planet’s poles slowly move so that the North Pole points to different stars over time, a motion called precession. This means the North Star we have now, Polaris, won’t always be our North Star. That creates subtle changes in the night sky over a 26,000-year period.

 

Precession and the path of the North Pole in the night sky.

 Our sun orbits the center of the Milky Way galaxy, so the exact pattern of stars in the night sky slowly changes. All other stars move under the various gravitational influences that direct their motions as they, too, orbit around the Milky Way.

 New stars are born and old stars die, sometimes with a dramatic effect.

 

The Great Nebula in Orion, where new stars are forming.

 

The Crab Nebula, the remains of a star that died in a supernova explosion.

 

Galaxies move through the universe, sometimes colliding. The larger galaxy then absorbs the smaller galaxy, gaining from the cannibalized galaxy the stars and gas clouds, the places where new stars come into being. Most of those new stars will have new planets orbiting them. Some of those planets will likely create new living beings.

Two galaxies colliding. They will eventually merge into one.

Change is the one constant in our lives. Even our night sky is eternally, if slowly, evolving.

This is the true magic of astronomy. You never get reruns. Each night remains unique. So, enjoy this night sky, because it will be different than any other night throughout time.