Thursday, May 10, 2018

Visions of a Red Planet

Visions of a Red Planet
Map image:
Percival Lowell, “Globe of Mars, longitude 270ยบ, 1909,”
Hubble Image:
NASA / J. Bell (Cornell) / M. Wolff (SSI)
150 years ago, were I to tell you that someday people would walk on the Moon you might not have believed me. Surrounded by horses and steam, it may well have seemed an impossible dream. Now, nearly 50 years after the first footsteps in lunar dust, our collective perspective has shifted. Today the question isn’t “Will people walk on Mars?” Instead, it’s “Who will be the first?” The technological challenges of traveling to the red planet and returning to the blue are significant, to be sure, but we believe not insurmountable. The biggest question that remains is will it be this generation or the next willing to dedicate the effort to the take the next steps through the solar system.

With this in mind, let us take the occasion of this summer to reflect upon how our knowledge of the red planet has exploded in the last 100 years.

Why this summer? Because geometry.

Both Earth and Mars orbit the Sun in nearly perfect circles, the key word being “nearly”. These "not quite circles" are called ellipses. You can think of an ellipse as sort of a squashed circle. The Sun offset from the center of the orbital ellipses of the planets. The Earth orbits at an average distance from the Sun of about 93 million miles. But because of its elliptical orbit, Earth is actually a little bit closer to the Sun in January, and a little bit further away in July.
The relative positions of Earth and Mars over
a two year period. Image not drawn to scale.

Mars orbits 150 million miles from the Sun, and takes nearly twice as long to orbit the Sun than Earth does. Roughly every two years, the Earth and Mars end up being on the same side of the solar system. When Earth passes Mars in its orbit, Mars will appear directly opposite the Sun in the sky. Astronomers call this “opposition” and when a planet is at opposition it will also be at its closest point to Earth. That’s great news to astronomers who want to look at Mars. Being closer to Earth, Mars will appear bigger and brighter in the telescope.

Sometimes, if astronomers are really lucky, the opposition of Mars will happen just as the Earth is at the furthest point from the Sun in its orbit, and Mars at its nearest point. That cuts a few million more miles off the distance between the two planets, making the red planet appear even brighter in the sky. That’s what happening this summer, making it an excellent time to go out and observe Mars.

What does Mars look like and what can you expect to see this summer?

This photograph of Mars taken during the 2003 opposition
is a good example of the kind of view to expect this summer.
Image Credit: Philipp Salzgeber CC-BY-SA 2.0
Mars is small. It’s a smaller planet than the Earth, but it has about the same land area. If you took all the continents on Earth and crashed them together, you’d get something about the size of Mars. And Mars is far away, even at its closest point. 36 million miles might be spitting distance in the solar system, but it’s still pretty far for human eyes to see. Through a small to medium sized telescope, an observer mostly sees a small, fuzzy, red disc.

Before Cameras were invented, people drew pictures of what they saw to record what was visible in the telescope. They would wait for the brief moments when the air would steady and calm, and then map Mars as accurately as they could. Of course, they were still looking at a small, fuzzy, red disc so they only saw clear glimpses of the planet only briefly. The human brain is incredible at detecting patterns, ocassionally even detecting patterns where no pattern exists. Anyone who’s ever fallen for an optical illusion has experienced this before. Fuzzy data plus a pattern-detecting computer that sometimes gets things wrong can lead to bad conclusions.

The Italian astronomer Giovanni Schiaparelli thought he saw grooves or channels cutting through the Martian surface during the opposition of Mars in 1877. He used the Italian word “canali” to describe them. This word was mistranslated into English not as “channels” but as “canals”. Channels could be formed naturally from the movement of wind or water. But canals? Canals are built by people.

Map of the "Canals" on Mars drawn by Percival Lowell
in his book Mars published 1895.
American businessman Percival Lowell became so obsessed with Schiaparelli’s canals, that he eventually built his own observatory in Arizona, the Lowell Observatory. He believed the canals were a product of a Martian civilization building a vast network of aqueducts. These transported water from the ice caps of the planet to the desert-like regions near the equator. He drew maps of the huge engineering project he believed he saw spider-webbing across the surface. The network of canals didn’t actually exist.

While the scientifc consensus had been that the canals were merely optical illusions for some time, it wasn’t until the Mariner spacecraft missions of the 1960s and 70s that the idea of Martian canals was finally put to rest for good. These probes found no hint of a Martian civilization, but the world they did reveal was perhaps just as interesting as the one some hoped they would find.

Mars was engulfed by a huge dust storm when Mariner 9 entered orbit around the planet in 1971. Mariner 9 was the first spacecraft to orbit another planet, and scientists hoped it would send back the clearest pictures ever seen of Mars. The dust storm made it impossible to see the surface. The scientists waited months for the air to clear. In January 1972, as the dust was still slowly settling out of the atmosphere, Mariner started sending back images. The peaks of four mountains began to peek past the cloud tops. The mountains were tall, very tall. They would have had to tower above the surface. Each had to be about 20 kilometers tall to poke out through the clouds. The tallest was nearly 25 kilometers tall, two and a half times the height of the tallest mountain on Earth. Mars was going to be full of surprises.
Olympus Mons (lower right) is the largest volcano in the solar system at a towering 25 kilometers tall,
two and a half times as tall as Mount Everest.
Image Credit: ESA / DLR / FU Berlin (G. Neukum) / Justin Cowart CC-BY-NC-SA-3.0

As the storm continued to dissipate, the dust lingered in the lowlands. It revealed the presence of a gash in the planet’s crust 8 kilometer deep, four times deeper than Arizona’s Grand Canyon, and nearly as wide as North America. The network of deep chasms that spanned one-quarter the distance around Mars was named the Valles Marineris, or Mariner Valley, after the spacecraft that discovered it. Mariner’s photos revealed a cold desert world, and paved the way for future missions to land on the surface.
The Valles Marineris canyon system stretches over 2,400 miles long
and reaches depths of 23,000 ft.
Image Credit: NASA / JPL-Caltech

This self-portrait taken by Opportunity features the rover still
on its landing stage. The airbags are visible peeking out from behind
the lander petals. Image Credit: NASA / JPL
Each mission to Mars incrementally furthered our understanding of the red planet. Viking showed we could do useful science on the surface. Mars Pathfinder proved we could land cheaply. Mars Odyssey, Mars Global Surveyor, and Mars Reconnaissance Orbiter provided better and better images of the surface from space. Then came the rovers. Landing in January 2004, the Mars Exploration Rovers Spirit and Opportunity were designed to work for 90 Martian days, called 'sols'. Spirit worked for more than 6 years, and finally ceased functioning in 2010 after getting caught in a sand dune. Opportunity is still operating, and as of May 1, 2018 is on sol 5071 of its 90-sol mission. Both rovers sent back evidence supporting the idea that liquid water was present on the surface of Mars sometime in the distant past.

The most recent rover to touch down on the red planet is the Mars Science Laboratory Curiosity. Curiosity landed in 2012 at Gale Crater. Since then it has been climbing the tall mountain located in the center of Gale Crater named Mount Sharp. By analyzing the rock formations that make up Mount Sharp, Curiosity has found evidence that Gale Crater was once filled with a lake of liquid water that may have had conditions suitable for life.
The rim of Gale Crater is visible in the distance in this image taken by the Mars rover Curiostiy.
Image Credit: NASA / JPL-Caltech / MSSS / Damia Bouic

Each successful mission to Mars has increased our understanding of our neighbor planet, and each one brings us closer to sending the first people to land there. Every photograph sent back has revealed more of that distant world, and has transformed Mars from merely a red point of light in the sky to a place as real as any on the Earth. No longer consigned to the imaginations of science fiction authors, Mars is a destination for future human explorers.

This mosiac showing a full hemisphere of Mars was created from 102 images taken by the Viking orbiters.
The Valles Marineris is visible center, and at the left of the images are the three volcanoes of the Tharsis Plateau.
Image Credit: NASA / JPL-Caltech
As part of observing the opposition of Mars this summer, the Delta College Planetarium and Learning Center will be hosting an exhibition of photographs taken of Mars. Visions of a Red Planet: The Photography of Martian Exploration features stunning images of Mars taken by orbiting spacecraft as well as surface robots. The exhibit runs May 11 through September 1, 2018. Located in the planetarium main lobby, the exhibit is free during all public open hours.

Friday, January 19, 2018

Identifying Meteorites

All About Meteorites

Photo: Meteor, 8.5.2016 by Migebuff. CC-BY-SA 4.0
There is just something about meteorites. Something deep within us stirs when we hold a rock from “outer space.” Or when we realize that the lump of stone in our hand is billions of years old. It is no wonder that so many people are searching to find their own meteorite. How do you know if you find one? Could that black rock in the garden be a meteorite? It looks interesting. How could you even tell? We at the Delta College Planetarium are here to help give you the knowledge to do a first pass and filter out the regular old earth rocks from the specimens that deserve further scrutiny.

What are meteorites? Are they different from meteors and where do they come from? Astronomers use the word “meteor” to mean one very specific phenomenon; the bright quick streaks of light we occasionally see in the night sky, sometimes called “shooting stars”. Meteors occur when tiny bits of dust and rock slam into the Earth’s atmosphere. The dust or rock itself is called a “meteoroid”. When the meteoroid collides with the atmosphere it quickly rams into the air in front of it. As the air is compressed, it heats up so much that it glows white-hot. This glowing event is a “meteor”.

Most meteoroids end their stories here. The air radiates enough energy to melt and break up the meteoroid. However, some meteoroids are large enough, and strong enough that they survive the shock of entering the Earth’s atmosphere. If a meteoroid survives to the surface, that object graduates to being a “meteorite.”

Basalt is common earth rock that is frequently
misidentified as a meteorite.
Photo: Basalt by James St John. CC-BY 2.0

Meteorites are special because they do not look anything like Earth rocks, chemically speaking. The chemical and physical properties that formed them do not exist on the Earth. Most meteors started their lives in the asteroid belt between the orbits of Mars and Jupiter. In rare cases, a meteorite might have originated from a planetary body, like the Moon or Mars.

A stony meteorite specimen that fell near Tindouf, Algeria.
Photo: NWA869 Meteorite by H Rabb. CC-BY-SA 3.0

Meteorites come in three basic flavors. The first is stony meteorites. These are, true to their name, mainly made of stony materials. These are by far the most common kind of meteorite, but they can be difficult to detect because they frequently look like Earth rocks.

Example of a typical iron meteorite.
Photo: Octahedrite (Canyon Diablo Meteorite) (4.55 Ga) 2
by James St John. CC-BY 2.0

The second kind are iron meteorites. Unsurprisingly, these are made of iron. Far rarer than their stony cousins, iron meteorites are much easier to identify because of just how much iron there is in their chemical makeup.

Stony-iron meteorites feature nodules of minerals
surrounded by iron.
Photo: Pallasite-Esquel-RoyalOntarioMuseum-Jan18-09
by Captmondo. CC-BY-SA 3.0

The third kind of meteorite is sort of a mixture of the two previous types. They get the creative name stony-iron meteorites.

What about the black rock in the garden? Could it be a meteorite? Maybe. Many meteorites share common features that you can check for at home.

One common feature is meteorites tend to be heavy for their size, much heavier than you would expect from an Earth rock. This is because most meteorites have pure iron metal inside of them, even the stony ones. The presence of the iron also means most meteorites will react strongly to a magnet. If a magnet falls off or is only weakly holding on to the rock, then it is probably not a meteorite. In some cases, a stony meteorite might have almost no iron in it, and wouldn't react strongly to a magnet. In those instances, look for other strong indicators of extraterrestrial origin, such as a fusion crust, decribed below.

The iron present in even a stony meteor will have formed into small irregular blobs distributed throughout the specimen. You can scratch the suspected meteorite with a file looking for these blobs. They will appear as bright, shiny metal similar in appearance to chrome. Just a faint metallic sheen will not do, it should shine brightly.
Note how the bright iron blebs are spread randomly through the meteorite.
Iron rich rocks on the earth lack this irregular distribution.
Photo: Fisher by Jon Taylor. CC-BY-SA 2.0

If your suspected meteorite fell from space, it will likely have a layer of fused rock on the outside, called the “fusion crust”. Some meteors break up after the point where a fusion crust would form, exposing some of the inside of the meteorite, but most meteorites will have some of this fusion crust over part or the entire meteorite. The crust forms from the molten rock that develops on the outside as the meteoroid moves through the atmosphere. It will appear dark grey to charcoal black in color. The crust is usually quite thin, only a few millimeters deep. Lines might be present from the flow of hot gasses over the meteorite.
The fine lines in the fusion crust mark where channels of hot gases flowed over
the meteorite while it was entering the atmosphere.
Photo: Allende meteorite, crusted individual, 5g by Jon Taylor. CC-BY-SA 2.0

Smooth divots can appear in the surface of a meteorite, called thumbprints. The surface of a meteorite should still appear relatively smooth and rounded. Remember, this object plunged through the atmosphere. Atmospheric entry will have blasted away any hard angles or sharp edges. There also should be no bubbling or air pockets; these are telltale signs that a rock formed on the Earth.
These divits are called thumbprints because they resemble the mark left behind
when sticking one's thumb into clay.
Photo: Sikhote Alin Meteorite by H. Rabb. CC-BY-SA 3.0

Even though the air sculpts meteorites as they move through the atmosphere, they rarely form aerodynamic shapes. Meteorites are usually irregularly shaped with rounded points, so they are almost never round. Round metallic objects are frequently from human manufactured origins.

Having never been exposed to air, the iron in meteorites is completely unoxidized. Once it becomes exposed to the Earth’s atmosphere, the iron in the meteorite will quickly begin to rust. Suspected meteorites should show signs of this rusting, frequently turning the common rusty red color.

You can also perform a streak test. Take an inexpensive, unglazed, white ceramic tile from a home improvement store and drag the suspected meteorite across the tile. What color streak did the rock leave behind? If the streak is brown, it might be a meteorite. Meteorites produce a brown colored powder when finely ground. If the color is red or black, it is unlikely to be a meteorite and is probably some form of Earth rock.

Does it mean that a rock that passes all these tests is a meteorite? Meteorites are quite rare and Earth rocks can masquerade as them well enough to pass these tests. Ultimately, the only way to know for sure is to test the sample’s chemical composition in a laboratory.

Tuesday, February 14, 2017

Get Ready for the August Solar Eclipse!

On August 21, 2017, in some parts of the United States around mid-day, the Sun is going to disappear. Then, about 2 minutes later, it is going to come back. How is the Sun going to accomplish this “vanishing trick?” On that day, the Moon will move into just the right position to completely block the disk of the Sun seen from parts of the United States. We call this a total solar eclipse.

What is a Solar Eclipse?

Solar eclipses happen when the Moon passes between the Sun and the Earth. The Moon doesn’t sit perfectly on a line drawn between the Sun and the Earth. Instead, it orbits at an angle of about 5 degrees with respect to that line.

Image Credit: SMU Physics
Usually when the Moon passes between the Sun and the Earth it will pass above or below the Sun as seen from the Earth because of that angle. However, when the Moon is at just the right spot in its orbit at just the right time, it will actually block the Sun as seen from the Earth. The Earth passes into the Moon’s shadow. The Moon is a lot smaller than the Earth, so the shadow the Moon casts is also a lot smaller. In fact, the Moon is so far away, and so small, that the darkest part of its shadow, called the umbra, just barely reaches the Earth. If an observer is standing on the Earth in the path of the Moon’s umbra, they will see the Moon totally cover the disk of the Sun. Astronomers call the line traced by the Moon’s umbra the “path of totality.”

Image Credit: The New Student's Reference Work, 1914

But how can that be? Isn’t the Sun really, really big? And the Moon, it’s even tinier than the Earth! How could it cover up something as big as the whole Sun? It is all about being at the right place at the right time. The Sun is about 400 times bigger than the Moon, but the Sun is also about 400 times further away from Earth than the Moon is from the Earth. From the surface of the Earth, the Sun and Moon look nearly the same size in our sky, even though if we could place them side by side it wouldn’t even be close.

Why is this eclipse special?

Total solar eclipses are not incredibly rare. They occur every few years. However, the path of a total solar eclipse is tiny compared the surface of the Earth, so an eclipse being visible from any particular point on the Earth is quite rare. The last total solar eclipse to happen in the United States was in 1991 (and then only in Hawaii), and the next one won’t occur until 2024.

What makes this solar eclipse special is that the path of totality stretches across all of North America, from Oregon to South Carolina. This means that nearly every person in the United States will be within a day’s drive from seeing a total solar eclipse.

Anyone standing in the thick yellow line in the middle of the map will see a total solar eclipse. Those outside the yellow line will not be able to see Moon completely cover the Sun, and will only see a partial solar eclipse.

Where can I see the eclipse?

The closest place to Bay City to see the total eclipse will be in southern Illinois, about 600 miles away. That is pretty far away, but if you do make the journey you will be treated to a special sight that not many people get to see.

Maybe southern Illinois is too far away, is it even worth trying to see the eclipse from Bay City? Yes! While you won’t be able to see the Moon completely cover the Sun from Michigan, you will be able to see the Moon cover nearly the entire disk of the sun. This is a partial solar eclipse. The Moon will cover over 80% of the Sun at the height of the eclipse from Bay City. For those that want to see the total event but can’t get to the path of totality, or those that find themselves looking up into clouds, the eclipse will also be streamed live on the internet.

How do I view the eclipse safely?

The first rule of viewing an eclipse is never look directly at the Sun. Looking directly at the Sun can permanently damage your eyes.

The second rule is NEVER EVER look at the Sun through any kind of magnifying device (such as binoculars or a telescope) that does not have a proper solar filter securely installed on it. Looking at the Sun through an unfiltered telescope WILL damage your eyes, quickly and permanently. If you are not sure if something is a proper solar filter, do not use it.

Eye protection when viewing the Sun is very important. Although invisible, sunlight contains dangerous infrared and ultraviolet rays. These rays of light are damaging to the human eye, so observers need to take special precautions. Solar eclipse glasses are an inexpensive option. These glasses are made with a thin plastic filter that blocks out nearly all the of the Sun’s light, including all of the dangerous rays, and allows a person to look directly at the Sun safely.

Do not use sunglasses! They will not block enough of the harmful rays of the Sun to protect your eyes. No, two pairs isn’t good enough either. There is no number of sunglasses you could wear to protect your eyes from the harmful rays of the Sun.

Image Credit: flickr user Mr.TinDC, CC-BY-ND 2.0
Special solar filters for telescopes and binoculars can be used to view magnified images of the Sun. Only use filters that cover the entire aperture of the telescope. Never use a solar filter that attaches to an eyepiece, as they are prone to failure and can quickly damage your eyes. Not sure if your filter is a solar filter? Ask an astronomer. Always inspect your filter for cracks and pinholes before using. Never look through a telescope with a filter you are not 100% sure will protect your eyes.

But what if you don’t have solar eclipse glasses or a proper solar filter for your telescope or binoculars? There many indirect viewing techniques you can use. You can build a pinhole viewer out of a box and some tin foil. The viewer will project an image of the Sun on to another surface that is safe for viewing. You can also use a telescope to project an image of the Sun onto another surface, but there are a couple of things to consider before using this method. All that energy from the Sun’s light is passing through the lenses or reflecting off the mirrors of the telescope. This could cause them to heat up and crack, damaging the telescope. There will also be a dangerous beam of light from the telescope’s eyepiece to the projection surface where all of the harmful rays of the Sun will be concentrated. Do not stick your eye or skin in that beam, as it could injure you easily. With those considerations in mind, telescopic projection can be a safe technique for viewing a magnified image of an eclipse.

What will I see during the eclipse?

Image Credit: Tom Ruen, CC BY-SA 4.0
The Moon will slowly creep in front of the Sun. It will take the Moon nearly 90 minutes to cover the Sun. For most of the process, there will be no noticeable darkening of the surrounding area.

Image Credit: Arief R. Sandan (Ezagren), CC BY 1.0
About 15 minutes before totality, it will begin to get noticeably darker outside. As the Moon moves to cover the entire Sun, the remaining portion of the Sun will look as though it were a string of beads. These are called “Baily’s beads,” and are caused by portions of the Sun still being visible between mountains on the Moon. When only one Baily’s bead remains, the eclipse may resemble a diamond ring.

Image Credit: Luc Viatour /, CC BY-SA 3.0
When the moon finally covers the sun, it will get very dark out. The stars will be visible, and the surrounding horizon will look like sunset. Around the edge of the Moon, you will be able to see the Sun’s corona, the outer layers of the Sun’s atmosphere. Usually the Sun is so bright that it washes out any view of the corona, but because of the eclipse you will be able to see this feature with your own eyes. During totality, the eclipse is safe to look at without eye protection. But still take care, because as soon as any part of the Sun reappears from behind the Moon, so do those dangerous infrared and ultraviolet rays. The exact length of the totality will depend on your location, but for most places in the path of totality it will be longer than 2 minutes.

Then, as the Moon moves along its orbit, the Sun will peak out, spilling its light all around. Baily’s beads will be present again, and it will take about 90 minutes for the Moon to exit the disk of the Sun.

Where can I learn more about the eclipse?

Stop by the Delta College Planetarium. We’re always ready to answer your questions. Our new show Eclipse: The Sun Revealed, opening Saturday, May 13, is all about the science and history behind solar eclipses.

Another fantastic resource is There you will tons of great maps and information leading up to the August 21, 2017 solar eclipse.