Posted on by Steve Nerlich

Astronomy Without A Telescope – No Metal, No Planet

The spiral galaxy NGC 4565, considered a close analogue of the Milky Way and with distinctly dusty outer regions. Credit: ESO.

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A Japanese team of astronomers have reported a strong correlation between the metallicity of dusty protoplanetary disks and their longevity. From this finding they propose that low metallicity stars are much less likely to have planets, including gas giants, due to the shorter lifetime of their protoplanetary disks.

As you are probably aware, ‘metal’ is astronomy-speak for anything higher up the periodic table than hydrogen and helium. The Milky Way has a metallicity gradient – where metallicity drops markedly the further out you go. In the extreme outer galaxy, about 18 kiloparsecs out from the centre, the metallicity of stars is only 10% that of the Sun (which is about 8 kiloparsecs – or around 25,000 light years – out from the centre).

This study compared young star clusters within stellar nurseries with relatively high metallicity (like the Orion nebula) against more distant clusters in the outer galaxy within low metallicity nurseries (like Digel Cloud 2).

The study’s conclusions are based on the assumption that the radiation output of stars with dense protoplanetary disks will have an excess of near and mid-infra red wavelengths. This is largely because the star heats its surrounding protoplanetary disk, making the disk radiate in infra-red.

The research team used the 8.2 metre Subaru Telescope and a procedure called JHK photometry to identify a measure they called ‘disk fraction’, representing the density of the protoplanetary disk (as determined by the excess of infra red radiation). They also used another established mass-luminosity relation measure to determine the age of the clusters.

Graphing disk fraction over age for populations of Sun-equivalent metallicity stars versus populations of low metallicity stars in the outer galaxy suggests that the protoplanetary disks of those low metallicity stars disperse much quicker.

Left image - The Subaru Telescope in Hawaii. Credit: NAOJ. Right image - the relationship between disk persistence for low metallicity stars (O/H = -0.7, red line) and stars with Sun-equivalent metallicity (O/H = 0, black line). The protoplanetary disks of low metal stars seem to disperse quickly, reducing the likelihood of planet formation. Credit: Yasui et al.

The authors suggest that the process of photoevaporation may underlie the shorter lifespan of low metal disks – where the impact of photons is sufficient to quickly disperse low atomic mass hydrogen and helium, while the presence of higher atomic weight metals may deflect those photons and hence sustain a protoplanetary disk over a longer period.

As the authors point out, the lower lifetime of low metallicity disks reduces the likelihood of planet formation. Although the authors steer clear of much more speculation, the implications of this relationship seem to be that, as well as expecting to find less planets around stars towards the outer edge of the galaxy – we might also expect to find less planets around any old Population II stars that would have also formed in environments of low metallicity.

Indeed, these findings suggest that planets, even gas giants, may have been exceedingly rare in the early universe – and have only become commonplace later in the universe’s evolution – after stellar nucleosynthesis processes had adequately seeded the cosmos with metals.

Further reading: Yasui, C., Kobayashi, N., Tokunaga, A., Saito, M. and Tokoku, C.
Short Lifetime of Protoplanetary Disks in Low-Metallicity Environments

Posted on by Tega Jessa

Why is the Earth Tilted?

Winter Solstice
Earth as viewed from the cabin of the Apollo 11 spacecraft. Credit: NASA

Have you ever wondered why the Earth is tilted instead of just perpendicular with its plane of orbit? Scientists have taken a crack at answering that question. The main consensus is that it has to do with Earth’s formation along with the rest of the planets in the Solar system. This time in cosmic history is still a mystery to us but we do have some ideas about what went on. We know that the birth of the Sun created a new source of gravity in the young Solar System. The tidal forces between the young sun and the rest of the nebula the Sun was born from created further instability in the gases and dust left in the nebula. This allowed for the steady formation of the planets.

After millions of years passed enough matter collided to gain mass and its own gravity and become small versions of planets called planetessimals and protoplanets. These pre-planets collided to create even larger planets. This set the stage for how the Earth approached its final form. It looks like it probably collided with a another proto-planet and in the process it was tilted.

All the same the Earth’s tilt is very important. It is perfectly positioned so that it gives us the seasons and on top of that the seasons are near perfectly calibrated for life. When compared with other planets Earth’s tilt allows for season that are not too extreme in temperature but are pretty well balanced. At the same if it had stay in the “perfect” position one side of the Earth would be too hot at time and then too cold.

We have written many articles about the Earth’s tilt for Universe Today. Here’s an article about why Earth has seasons, and here’s an article about the Earth’s axis.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Posted on by Tega Jessa

Why is the Center of the Earth Hot

Earth's core.
Earth's core.

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It interesting that we have explored further into space than we have explored the depths of the Earth. The main reason for that is the pressure and the heat. We know through seismography that temperatures in the inner parts of the Earth actually exceed the surface temperature of the Sun! That is pretty hot. So why is the center of the Earth Hot. The answer comes from a lot different sources. The first is heat left over from the formation of the Earth. The next source is gravitational pressure put on core by tidal forces and the rotation of the Earth. The last known source of heat is the radioactive decay of elements in the inner part of the Earth.

The Earth is pretty old at 4 billion years old and there are still things we don’t completely understand about its formation. We do know that gravity played a role pulling in more matter and compressing it to form the Earth. When you have matter colliding at high velocities like it did in the early stages of the Solar System’s development all that kinetic energy has to go somewhere. In the case of Earth that energy was turned into heat. This heat is the initial source for the temperatures in the Earth’s interior.

The next source of heat is gravitational pressure. The Earth is under immense pressure due to the tidal forces exerted by the Sun, the Moon, and the other planets in the Solar System. When you include the fact that it is also rotating the Earth’s core is under immense pressure. This pressure basically keeps the core hot in the same way as a pressure cooker. It also helps to minimize the heat it loses.

The last and most important source of heat is nuclear fission of heavly elements in the Earth’s interior. In short the Earth has a nuclear engine inside it. It is thank to the continous nuclear fission of elements in the Earth’s interior that replaces the heat the Earth loses keeping it nice and hot. This fission process occurs in the form of radioactive decay. It also creates the convection currents in the mantle that drive plate tectonics.

We have written many articles about the Earth’s core for Universe Today. Here’s an article about the Earth’s outer core, and here are some interesting facts about the Earth.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:
http://helios.gsfc.nasa.gov/qa_earth.html#hot
http://www.physorg.com/news62952904.html
http://www.ccmr.cornell.edu/education/ask/index.html?quid=215

Posted on by Jason Rhian

STS-133 Crew Conducts TCDT Training

The crew of STS-133 discusses their perspectives on the final flight of space shuttle Discovery with the media. Photo Credit: Universe Today/awaltersphoto.com

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The crew for the last mission for space shuttle Discovery spent the week at NASA’s Kennedy Space Center conducting the Terminal Countdown Demonstration Test or as it is more commonly know – TCDT. The crew arrived Tuesday, Oct. 12 and immediately set to work. This week of training is the last major milestone on the path to launch, currently scheduled to take place on Nov. 1 at 4:40 p.m. EDT.

TCDT consists of is training that simulates the final hours up until launch. This provides training for both the crew and the launch team. The launch team practices launch day timelines as well other, crucial flight-day procedures. The crew on the other hand went through a number of exercises that included:

• Rescue training – The astronauts will run through several simulations where they practice what to do in the event of an emergency. The crew will be instructed on how to use the emergency baskets that will allow them to escape the launch pad in case there is a fire. They will also learn how to operate the tank-like M113 personnel carrier and other emergency equipment.
• The commander in pilot will perform abort landings and other flight aspects in the Shuttle Training Aircraft (STA). The plane is a Grumman Gulfstream II and it duplicates the shuttle’s approach profile and many of the orbiter’s handling qualities.
• Conduct a launch day simulation that includes everything that will happen on launch day – except the launch. The crew walked out in their bright orange launch and entry suits. TCDT also includes a simulated abort so that the crew is well-versed as to what do to in case of that scenario.

STS-133 crew members arrive at NASA's Kennedy Space Center in their sleek T-38 jets. Photo Credit: Universe Today/awaltersphoto.com

These activities allow the crew and flight teams to do a rehearsal of all the events that will take place on launch day.

“This is a dress rehearsal for the real flight so the crew is kind of peaked up; they’ve put all the sequence of events together, when they go out to the pad they’ll do everything except igniting the main engines,” said Robert Springer a two-time shuttle veteran. “It’s a chance to review all your procedures and make sure everything is in place.”

The crew of STS-133 consists of Lindsey, Pilot Eric Boe and Mission Specialists, Michael Barratt, Tim Kopra, Alvin Drew and Nicole Stott. The crew is comprised entirely of space flight veterans.

NASA's official crew portrait of the crew of STS-133. Image Credit: NASA
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STS-133 is an 11-day mission to the International Space Station (ISS) to deliver the Leonardo Permanent Multipurpose Module (PMM) which contains, among other thing, the first humanoid robot to fly into space – Robonaut-2 (R2). Also onboard is the Express Logistics Carrier-4 and spare parts for the orbiting laboratory.

Springer’s first flight was on space shuttle Discovery and as he watched the crew for her final mission his thoughts reflected on his experiences and the end of the shuttle era.

“It’s going to be a little tough, my personal experiences that I have of Discovery and my memories that I have of that time make it a little bittersweet to realize that this will be the last time that Discovery will go into space.”

Posted on by Jon Voisey

Probing Exoplanets

Sometimes topics segue perfectly. With the recent buzz about habitable planets, followed by the raining on the parade articles we’ve had about the not insignificant errors in the detections of planets around Gliese 581 as well as finding molecules in exoplanet atmospheres, it’s not been the best of times for finding life. But in a comment on my last article, Lawrence Crowell noted: “You can’t really know for sure whether a planet has life until you actually go there and look on the ground. This is not at all easy, and probably it is at best possible to send a probe within a 25 to 50 light year radius.”

This is right on the mark and happens to be another topic that’s been under some discussion on arXiv recently in a short series of paper and responses. The first paper, accepted to the journal Astrobiology and led by Jean Schneider of the Observatory of Paris-Meudon, seeks to describe “the far future of exoplanet direct characterization”. In general, this paper discusses where the study of exoplanets could go from our current knowledge base. It proposes two main directions: Finding more planets to better survey the parameter space planets inhabit, or more in depth, long-term studying of the planets we do know.

But perhaps the more interesting aspect of the paper, and the one that’s generated a rare response, is what can be done should we detect a planet with promising characteristics relatively nearby. They first propose trying to directly image the planet’s surface and calculate the diameter of a telescope capable of doing so would be roughly half as large as the sun. Instead, if we truly wish to get a direct image, the best bet would be to go there. They quickly address a few of the potential challenges.

The first is that of cosmic rays. These high energy particles can wreak havoc on electronics. The second is simple dust grains. The team calculates that an impact with “a 100 micron interstellar grain at 0.3 the speed of light has the same kinetic energy than a 100 ton body at 100 km/hour”. With present technology, any spacecraft equipped with sufficient shielding would be prohibitively massive and difficult to accelerate to the velocities necessary to make the trip worthwhile.

But Ian Crawford, of the University of London, thinks that the risk posed by such grains may be overstated. Firstly, Crawford believes Schneider’s requirement of 30% of the speed of light is somewhat overzealous. Instead, most proposals of interstellar travel by probes generally use a value of 10% of the speed of light. In particular, the most exhaustive proposal yet created, (the Daedalus project) only attempted to achieve a velocity of 0.12c. However, the ability to produce such a craft was well beyond the means at the time. But with the advent of miniaturization of many electronic components, the prospect may need to be reevaluated.

Aside from the overestimate on necessary velocities, Crawford suggests that Schneider’s team overstated the size of dust grains. In the solar neighborhood, dust grains are estimated to be nearly 100 times smaller than reported by Schneider’s team. The combination of the change in size estimation and that of velocity takes the energy released on collision from a whopping 4 x 107 Joules, to a mere 4.5 Joules. At absolute largest, recent studies have shown that the upper limit for dust particles is more in the range of 4.5 micrometers.

Lastly, Crawford suggests that there may be alternative ways to offer shielding than the brute force wall of mass. If a spacecraft were able to detect incoming particles using radar or another technique, it is possible that it could destroy the incoming particles using lasers, or deflect it using a electromagnetic field.

But Schneider wasn’t finished. He issued a response to Crawford’s response. In it, he criticizes Crawford’s optimistic vision of using nuclear or anti-matter propulsion systems. He notes that, thus far, nuclear propulsion has only been able to produce short impulses instead of continuous thrust and that, although some electronics have been miniaturized, the best analogue yet developed, the National Ignition Facility, is, “with all its control and cooling systems, is presently quite a non-miniaturized building.”

Anti-matter propulsion may be even more difficult. Currently, our ability to produce anti-matter is severely limited. Schneider estimates that it would take 200 terrawatts of energy to produce the required amounts. Meanwhile, the overall energy of the entire Earth is only 20 terrawatts.

In response to the charge of overestimation, Schneider notes that, although such large dust grains would be rare, but “even two lethal or severe collisions are prohibitory”, but does not go on to make any honest estimations of what the actual probability of such a collision would be.

Ultimately, Schneider concludes that all discussion is, at best, extremely preliminary. Before any such undertaking would be seriously considered, it would require “a precursor mission to secure the technological concept, including shielding mechanisms, at say 500 to 1000 Astronomical Units.” Ultimately, Schneider and his team seems to remind us that the technology is not yet there and that there are legitimate threats we must address. Crawford, on the other hand suggests that some of these challenges are ones that we may already be well on the road to addressing and constraining.

Posted on by Tega Jessa

Why Can We See the Moon During the Day?

Crescent Moon
Crescent Moon

We all know the basics of the Diurnal Cycle – day and night, sunrise and sunset. And we are all aware that during the day, the Sun is the most luminous object in the sky, to the point that it completely obscures the stars. And at night, the Moon (when it is visible) is the most luminous object, sometimes to the point that it can make gazing at the Milky Way and Deep-Sky Objects more difficult.

This dichotomy of night and day, darkness and light, are why the Moon and the Sun were often worshiped together by ancient cultures. But at times, the Moon is visible even in the daytime. We’ve all seen it, hanging low in the sky, a pale impression against a background of blue? But just what accounts for this? How is it that we can see the brightest object in the night sky when the Sun is still beaming overhead?

Continue reading “Why Can We See the Moon During the Day?”

Posted on by Tega Jessa

Where is Uranium Located

Periodic Table of Elements
Periodic Table of Elements

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Uranium is a silvery white metal and is number 92 on the table of periodic elements. It is a well-known element because of its radioactive properties which are used in nuclear reactor powered by nuclear fission. We know that this element is very sought after as source of power by many countries wanting to shift from oil and fossil fuel based economies. So where is Uranium located and how do miners harvest it?

To understand how it is found we need to learn about how it was discovered. Uranium was first discovered by German chemist martin Heinrich Klaproth in 1749 when he was heat treating Minerals. He named the new mineral produced Uranium. The first pure sample of Uranium metal was produced in 1841 by Eugène-Melchior Péligot an analytical chemist who was heat treating Uranium tetrachloride. Demand for Uranium outside its more mundane uses as a window dye was initiated by the discovery of its fissile nuclear properties by Enrico Fermi. Mr. Fermi would go on to lead the Manhattan Project in 1942 that lead to the creation of nuclear weapons and reactors. When the energy it produced was realized the demand for Uranium immediately increased.

So where is Uranium located? In space Uranium is formed naturally occurring in supernovas. However since we can’t even travel to the nearest star it is just a minor fact. On Earth Uranium is surprisingly plentiful for a heavy metal. In fact estimate place the Earth’s supply of Uranium at 30 times that of Silver. This is because Uranium can be found in topsoil anywhere on the planet as well as in the mantle. Scientist even theorize that the natural decay of Uranium and other radioactive elements is what heats the Earth’s core and mantle causing convection currents in the magma and creating plate tectonics.

Uranium can be found as part of a lot of different minerals such as uranite. The element rarely occurs in its pure form. Even then the more fissile kinds of isotopes aren’t plentiful in nature. Uranium ore is the main source of uranium even though with the discovery of how wide spread it is in the Earth’s crust and scientist are looking for inexpensive ways to process it from the soil. In the meanwhile Uranium ore can be found in mines in Canada, Russia, and in Sub-Saharan Africa.

We have written many articles about Uranium for Universe Today. Here’s an article about the lunar Uranium, and here’s an article about nuclear fission.

If you’d like more info on Uranium, check out Wikipedia, and here’s a link to the Encyclopedia of Earth.

We’ve also recorded an entire episode of Astronomy Cast all about the Atom. Listen here, Episode 164: Inside the Atom.

Sources:
Wikipedia
Encyclopedia of Earth
World Nuclear Association

Posted on by Tega Jessa

Where is the Ozone Layer Located

Ozone layer hole. Image credit: NASA
Ozone layer hole. Image credit: NASA

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The Ozone Layer is the portion of the atmosphere that contains high levels of the oxygen molecule ozone. This molecule plays an important role acting as a natural UV shield for the Earth. You may wonder where is the ozone layer located to play such a vital role so effectively. The Ozone layer is actually located in the stratosphere in a region that is 10 to 50 km above the Earth.

So why is the Ozone layer so important? As mention before the secret lies in oxygen molecules. Normal oxygen in its natural molecular state is made up of only two atoms. However this changes when oxygen in the thermosphere is exposed the Sun’s ultraviolet rays. The rays separate oxygen molecules the free oxygen joins with the remaining two atom oxygen molecules to create ozone. This process might seem simple but it helps to screen out 99.5 percent of the ultraviolet radiation that the Sun sends towards earth. The times that the ozone layer didn’t screen out this type of radiation at such levels life was almost wiped out according to the geologic record.

You might think that this is an exaggeration until you observe the biological damage UV rays can do. We have already seen the harm caused when people don’t take the proper precautions when going to the beach. The least harm comes in the form of sun burn. People overexposed to the UV rays that do make it to earth have their skin damaged by the UV energy that penetrates their skin. However it gets more serious the longer a person is exposed to UV rays. The reason is because the damage gets to the cellular level causing cancers and genetic damage. Essentially it’s like being exposed to a nuclear reactor in melt down. The high energy radiation over time would accumulate harm in living tissue until it killed the organism exposed to it.

Despite its importance industry produced and released chemicals into the air that interfered with the ozone cycle. The main problem chemical CFC’s prevented oxygen molecules from complete the bonding process that is important for the completion of the ozone cycle this caused a major depletion of ozone in key areas of the Earth’s atmosphere. This is huge when the natural concentration of ozone was already quite low. This just goes to show the delicate balance that was upset. Fortunately nations upon hearing the harm caused started bans on CFC’s while industry tried to find alternatives to use in products. The result started to show with ozone depletion actually slowing down and reversing with scientist predicting recovery within the next century.

We have written many articles about the ozone layer for Universe Today. Here’s an article about the depletion of the ozone layer, and here’s an article about the ozone layer.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Posted on by Nancy Atkinson

How to Deflect an Asteroid with Today’s Technology

Artist concept of a space tug. Credit: NASA

Apollo 9 astronaut Rusty Schweickart is among an international group of people championing the need for the human race to prepare for what will certainly happen one day: an asteroid threat to Earth. In an article on Universe Today published yesterday, Schweickart said the technology is available today to send a mission to an asteroid in an attempt to move it, or change its orbit so that an asteroid that threatens to hit Earth will pass by harmlessly. What would such a mission entail?

In a phone interview, Schweickart described two types of “deflection campaigns” for a threatening asteroid: a kinetic impact would roughly “push” the asteroid into a different orbit, and a gravity tractor would “tug slowly” on the asteroid to precisely “trim” the resultant change course by using nothing more than the gravitational attraction between the two bodies. Together these two methods comprise a deflection campaign.

Artist Impression of Deep Impact - Credit: NASA

“In a way, the kinetic impact was demonstrated by the Deep Impact mission back in 2005,” said Schweickart. “But that was a very big target and a small impactor that had relatively no effect on the comet. So, we haven’t really demonstrated the capability to have the guidance necessary to deflect a moderately sized asteroid.”

Most important, the gravity tractor spacecraft would arrive prior to the kinetic impactor, precisely determine the asteroid’s orbit and observe the kinetic impact to determine its effectiveness. Following the kinetic impact it would then determine whether or not any adjustment trim were required.

“You want to know what happens when you do a kinetic impact, so you want an ‘observer’ spacecraft up there as well,” Schweickart explained. “You don’t do a kinetic impact without an observation, because the impactor destroys itself in the process and without the observer you wouldn’t know what happened except by tracking the object over time, which is not the best way to find out whether you got the job done.”

So, 10-15 years ahead of an impact threat — or 50 years if you have that much time — an observer spacecraft is sent up. “This, in fact, would also be a gravity tractor,” Schweickart said. “It doesn’t have to be real big, but bigger gets the job done a little faster. The feature you are interested in the outset is not the gravity tractor but the transponder that flies in formation with the asteroid and you track the NEO, and back on Earth we can know exactly where it is.”

Schweickart said even from ground tracking, we couldn’t get as precise an orbit determination of an NEO as we could by sending a spacecraft to the object. Additionally, generally speaking, we may not know when we send an observer spacecraft what action will be required; whether an impact will be required or if we could rely on the gravity tractor. “You may launch at the latest possible time, but at that time the probability of impact may be 1 in 5 or 1 or 2,” Schweickart said. “So the first thing you are going to do with the observer spacecraft is make a precise orbit determination and now you’re going to know if it really will impact Earth and even perhaps where it will impact.”

Artist concept of an impactor heading towards an asteroid. Credit: ESA

After the precise orbit is known, the required action would be determined. “So now, if needed you launch a kinetic impactor and now you know what job has to be done,” Schweickart said. “As the impactor is getting ready to impact the asteroid, the observer spacecraft pulls back and images what is going on so you can confirm the impact was solid, –not a glancing blow — and then after impact is done, the observer spacecraft goes back in and makes another precision orbit determination so that you can confirm that you changed its velocity so that it no longer will hit the Earth.”

The second issue is, even if the NEO’s orbit has been changed so that it won’t hit Earth this time around, there’s the possibility that during its near miss it might go through what is called a “keyhole,” whereby Earth’s gravity would affect it just enough that it would make an impact during a subsequent encounter with Earth. This is a concern with the asteroid Apophis, which is projected to miss Earth in 2029, but depending on several factors, could pass through a keyhole causing it to return to hit Earth in 2036.

“So if it does go through that keyhole,” said Schweickart, “now you can use the gravity tractor capability of the spacecraft to make a small adjustment so that it goes between keyholes on that close approach. And now you have a complete verified deflection campaign.”

Schweickart said a Delta-sized rocket would be able to get a spacecraft to meet up with an asteroid. “A Delta rocket would work,” he said, “but if there is a more challenging orbit we might have to use something bigger, or we may have to use a gravity assist and do mission planning for type of thing which hasn’t been done yet. So we can get there, we can do it – but ultimately we will probably need a heavy lift vehicle.”
As for the spacecraft, we can use a design similar to vehicles that have already been sent into space.

“A gravity tractor could be like Deep Space 1 that launched in 1998,” Schweickart said. “ You can make any spacecraft into a gravity tractor fairly easily.”

Rusty Schweickart

But it hasn’t been demonstrated and Schweickart says we need to do so.

“We need to demonstrate it because we – NASA, the technical community, the international community — need to learn what you find out when you do something for the first time,” he said. “Playing a concerto in front of an audience is quite different from playing it alone in your house.”