Saturday, March 26, 2011
Sunday, March 20, 2011
The Messenger has arrived! As of 9:10 p.m. EDT on Thursday March 17th, NASA's Messenger spacecraft entered orbit around the planet Mercury and as of 9:45 p.m. rotated towards Earth and started transmitting data. MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging. The spacecraft was launched August 3, 2004 from Cape Canaveral, Florida with the mission to "unravel the mysteries of planet Mercury." Messenger has spent the last years circling through the inner solar system, performing flybys and gravity assists of Earth, Venus, and even Mercury itself until finally settling into orbit around the innermost planet. The spacecraft carries several instruments that will take images and measurements of the planet:
The Mercury Duel Imaging System (MDIS) consists of wide-angle and narrow-angle imagers that will map landforms and topographic features. The Gamma-Ray and Neutron Spectrometer (GRNS) will detect gamma rays and neutrons that are emitted by radioactive elements on the surface and use that to map relative abundances of different elements. The Magnetometer (MAG) will map Mercury's magnetic field and magnetized rocks in the crust. The Mercury Laser Altimeter (MLA) will beam light to the planet's surface and a sensor will collect any reflected light in order to gather further information about topography. The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) is an instrument that is sensitive to light in the infrared to ultraviolet range in the spectrum and so can measure the abundances of various atmospheric gases and minerals on the surface. The Energetic Particle and Plasma Spectrometer (EPPS) will measure the composition, distribution, and energy of charged particles in the magnetosphere. And finally, the Radio Science (RS) instrument will use the Doppler effect to measure changes in spacecraft's velocity and use that to study Mercury's mass distribution, including variations in the thickness of the crust.
Mercury is the planet closest to the Sun. It is small and extremely dense with a lot of metals, a thin crust, and a thin atmosphere. It is thought to have formed out of the solar nebula, the disk of gas and dust around the newly formed Sun, but it is not known whether or not the planet formed in the location that it is today. It is odd that one of the densest objects in the solar system formed so close to the Sun. There are several ideas out there to explain why. Because Mercury resembles a planet core rather than a whole planet some think it was originally a larger object that suffered an impact that knocked part of the surface off and/or required the planet to reform. Others think that the very active early Sun blasted off the crust early in Mercury's history. Despite this possibly violent possible history, the planet has formed a thin atmosphere. Now we're not talking rain, clouds, wind etc. like we are used to thinking of on Earth. Mercury's atmosphere is more like scattered particles that only occasionally come in to contact with one another, it is more like a gas layer close to the surface, or an "exosphere." That surface has a cracked, scorched look to it. It is thought that the planet's iron core froze (or solidified) and contracted. To visualize this think about a balloon tightly covered by a piece of cellophane, if you let air out of the balloon it creates space between itself and the cellophane, but the cellophane still wants to cling to the surface of the balloon and so develops cracks or folds in order to stay in place. This theory says that Mercury's crust did something similar when the core solidified (note: the presence of a magnetic field suggests that at least part of the core may be liquid). Add to that the impact craters similar to the ones you see on our Moon and you start to get a picture of the planet. Oh yeah, and did I mention the possibility of ice? Uh-huh, the planet closest to the Sun may have ice at its poles. The rotational axis is straight, not tilted like Earth's, and so the poles never see sunlight. Barring other factors, no sunlight equals very cold and that means there could be ice. Neat.
As you can tell, there's a lot of ideas and theories out there about Mercury. Our lack of information mainly comes from the fact that Mercury is very difficult to observe. Think about it. It is really close to the Sun, and the massive amount of light coming from the Sun tends to obscure a lot of the planet's features. If you try to observe it when the Sun is below the horizon, at night, you will find that the planet never gets more than 28 degrees above the horizon. Then add the fact that the planet is tidally locked to the Sun. Tidal locking is when an object takes as long to rotate around its axis as it takes to complete its orbit, just like our Moon to us (a 1:1 resonance). In the case of Mercury, the planet does not have an exactly circular orbit and actually rotates three times for every two orbits around the Sun, in a 2:3 resonance (a year is only one and a half days long!). That tidal locking means that Mercury is always presenting the same side to us. From the two high-speed flyby's by Mariner 10 spacecraft in 1974 and 1975 we have some images, but only of one side of the planet.
It is likely that Mercury is the key to us unlocking the mechanism of terrestrial planet evolution. Messenger will gather data that will help answer the questions of why is the planet so dense, what is its geologic history, what is the nature of the magnetic field, what is the structure of the core, what volatiles (gases etc.) are present and important, and if there is ice at the poles.
But Messenger will not be the last spacecraft to visit Mercury. The European Space Agency (ESA) in a joint mission with the Japanese Aerospace Exploration Agency (JAXA) will be launching the BepiColombo in 2014 that will arrive at Mercury in 2020. This mission will further study the planet's evolution, form, interior, structure, geology, composition, atmosphere, magnetosphere, and polar regions. Find out more about this mission at their website: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=30
Visit these Messenger websites to learn more about the spacecraft, the mission, and up to the minute information and images:
A few news stories about the newly attained orbit:
Learn more about Mercury:
and the Mariner Program:
(image from nasa.gov)
Friday, March 18, 2011
Tomorrow night (March 19th) will be a perfect night for a moonlit stroll. Not just any moonlit stroll but a Supermoonlit stroll. Now, we've all see the illusion where the moon looks huge in the night sky, and it is just that, an illusion.The Moon isn't actually bigger or smaller as it travels across the sky. Why you see the Moon looking huge when it is low on the horizon is an optical illusion owing to the circuitry in your brain. There is no clear consensus on why. It could be an Ebbinghaus Illusion - where identically sized objects appear to be different sizes when placed in different surroundings (click link for picture) - the objects of known size to your brain that are near the horizon (trees, houses, etc.) provide a false frame of reference for the size of the Moon. When the Moon is high in the sky you have no such references and so see the Moon as smaller. Another possibility is how our brains interpret foreground objects for reference in terms of distance and size. Foreground objects of known size appear to be far away and so when something large, like the Moon, appears behind it and even farther away but still appears big then we interpret is as being larger than it is.
In the case of tomorrow night's Moon, it will actually be larger in the sky. Our Moon has an elliptical orbit around the Earth with one side of the ellipse, perigee, about 31,000 miles (50,000 km) closer than the other side, apogee. The moon will be in the perigee part of the orbit which will take it closer to Earth than it has been in two decades, since March 1993. This means that the moon will appear about 14% bigger and 30% brighter than when the it is in apogee (other side of the ellipse). Admittedly, that isn't all that big of a difference. It can be tricky to even tell the change in size, especially if you have no scale for reference, but the best time to look will be when the moon is near the horizon. This will be when the illusion of a bigger moon mixes with the reality of a closer moon to produce an amazing view.
Oh, and no, there will not be any cataclysmic, apocalyptic results of a close moon. Only slightly stronger tides.
Here's some more info:
(image from universetoday article)
Thursday, March 10, 2011
I haven't done a why-people-find-other-people-attractive story in a while. So I started looking through the literature, typing various search terms into journal databases that in any other context than science might have gotten me spam filtered. One of the first studies that caught my eye was from 2003, and it correlated facial attractiveness and semen quality in adult human males and tested how women rate facial attractiveness in various stages of their menstral cycle. Interesting. That study lead me to a more recent study out of Australia that sought to replicate the 2003 experiment and determine the generality of the relationship between attractiveness and semen quality.
But, as usual, let's take a step back. Not quite as big of a step as usual since you can click any of the links below and get a nice little sexual selection primer, but instead look at sexual selection in terms of honest signaling. Consider this: In a species where females choose the males, she can choose any male from a pool of individuals of varying qualities. In otherwords, she can choose a male with characteristics she likes. Those male characteristics are linked to attributes of the male that the female can use to assess his quality. This is where the honesty part comes in to play. If that characteristic, or signal, is honest that means that the quality of the male is what she thinks it will be. That means, on average, a certain degree of these signals must be honest for this system to work, otherwise females would just ignore them. So what are these signals anyway? Well, it depends on what characteristic you are talking about. Sometimes the signal is costly like the peacock dragging around that giant tail or a frog producing a mating call that will also tell predators his location. Signals like these can be handicaps - see Zahavi's Handicap Principle or Grafen's model - in which only very fit males can handle the cost of a handicap (very fit = good quality). Other signals fall into Weatherhead and Robertson's Sexy Son Hypothesis (or Dawkin's The Selfish Gene) in which a female chooses a particular mate because his genes will produce male offspring with the best chance of reproductive success. Of course, the female can't see the genes themselves but if she chooses an attractive male she will have attractive offspring and thus be more likely of passing on her genes.
In the field of animal behavior, mate choice is a popular and well studied subdiscipline. Typically these types of experiments are conducted with animals, called mate choice experiments. You give an individual, usually female, a choice between potential mates with different characteristics (looks, smells, displays, etc.) and see which one she chooses. Now I know that I've posted several studies on sexual selection including ones on fruit flies, mollies (fish), cichlids (also fish), seahorses, and even algae. I've also done a few stories about mate selection in humans, typically about why men find women attractive in a series of posts I like to call "Groundbreaking science - men like boobs." And today's study fits within that topic.
This is a study that looked at the phenotype-linked fertility hypothesis in humans. In the case of humans studies have shown that both face and body attractiveness contribute to overall attractiveness. Logical. So in this study they collected ratings of both and combined them into a single attractiveness component. So what did they do exactly? They picked 118 herterosexual, caucasian men between the ages of 18-35. They had each participant photographed, full body length and face close-up, wearing a white shirt and dark-colored shorts standing in a neutral position. Then the men filled out a questionnaire regarding lifestyle factors such as cigarette use, dietary habits, etc. (as they could potentially affect semen quality), and recorded self-measured testes volume. And, as this study evaluates semen quality, they took a semen sample. From this sample factors such as sperm concentration, motility, and morphology could be quantified. Then they had females rate each male face and body for attractiveness, in terms of a short-term sexual partner, on a seven-point scale (1 = not attractive; 7 = very attractive). A second set of females, not using hormonal contraceptives, were asked to rate the photographs at high and low fertile points in their menstrual cycle.
The researchers found no associations between attractiveness and semen quality. They also found no relationship between semen quality and measures of masculinity, symmetry, or averageness. So basically, this study does not replicate the 2003 study, which did find such relationships, and suggests that attractiveness in human males does not provide women with cues to their reproductive potential. Why the difference between studies? Who knows. It could be rating scale, including bodies and not just faces, how time in the menstrual cycle was determined, the number of men included in the sample, or any of a number of factors. So we have two studies that found different results. Why present this study at all? It is a good example for replication in science and an interesting study. I guess the jury is still out on whether or not being attractive is a signal for reproductive quality. However, coming from a female prospective - looks aren't everything but good looks don't hurt.
Read the study here:
Peters, M., G. Rhodes, and L.W. Simmons (2008) Does attractiveness in men provide clues to semen quality? Journal of Evolutionary Biology: 21, 572-579. (DOI: 10.1111/j.1420-9101.2007.01477.x)
And here is the study that they replicated:
Soler, C. et al. (2003) Facial attractiveness in men provides clues to semen quality. Evolution and Human Behavior: 24, 199-207. (DOI: 10.1016/S1090-5138(03)00013-8)
(image from corbis images)
Friday, March 4, 2011
This video was a reply in the comments from the Scientists for Better PCR video post I put up some time ago. Rather than stay hidden away in the comments I thought it was time that this video had a post all it's own. It is a far out video explaining protein synthesis that is so 60's-70's hippie that I can't not share it. Peace.
A couple of years ago a study was published in The American Naturalist about an interesting fungal parasite known as Ophiocordyceps unilateralis. This fungus infects ants in the tribe Camponotini (carpenter ants) but does not kill them outright. Rather, the ant remains alive for a short time but the fungus is in control. The fungus compels the ant to crawl down from its nest in the high forest canopy down to the small plants of the understory. Then the fungus has the ant crawl onto the underside of a leaf, clamp down its mandibles, and then die. There the ant body will stay while the fungus continues to grow inside of its body, producing a hyphae and stroma (fruiting body) that grows right out of the ant's head. The stroma then releases spores on to the forest floor, spores waiting to infect the next unsuspecting ant passerby. You can see where the nickname "zombie ants" and "zombie fungus" came from. Now, this was not a previously unknown species of fungus but rather an unknown effect of the fungus on ants, a previously unknown part of the life cycle. What is truly amazing is the accuracy to which the fungus directed the ant. The ants always clamped on to the underside of a leaf and almost always on a leaf vein. The chosen leaf was about 25 centimeters above the ground, with 94-95% humidity, and between 20-30 Celsius. The fungus directs the ant to a location with the parameters that it needs to survive and reproduce.
Now a new paper in the journal PLoS ONE describes four new species belonging to the O. unilateralis species complex from the Atlantic rainforest in Brazil. The species are named according to their ant host species (specifically Camponotus rufies, C. balzani, C. melanoticus, and C. novograndadensis). Ultimately, this paper is just recognizing and naming new species. However, it helps to draw attention to the south-eastern region (Zona de Mata) of the State of Minas Gerais in Brazil, one of the most heavily degraded biodiversity hotspot on the planet. A total of 92% of this rainforest is gone, and four new species have just been discovered. How many more are there to find and how many have already been lost?
Want more zombie animals? Check out these:
The nematode-ant relationship in Central America
The emerald cockroach wasp (Ampulex compressa)-cockroach relationship in the Polynesian Islands.
The spider (Plesiometa argyra)-wasp (Hymenoepimecis argyraphaga) relationship in Costa Rica.
The list goes on and on; pill bugs and spiny-headed worms (Plagiorhychun cylin-draceus), grasshoppers (Melanoplus sanguinipes) and the protist (Nosema acridophagus), the fluke (Dicrocoelium dendriticum) and the ant, the wasp (Glyptapanteles) and the caterpillar, the distome (Leucochloridium paradoxum) and the snail, the barnacle (Sacculina carcini) and the crab, etc. Wasps, ants, and caterpillars tend to have a lot of parasite-host stuff going on (there's even a whole group of parasitoid wasps), although admittedly not all that much zombism. It is an ever-so-interesting evolutionary arms race!
Read more about zombie animals here: http://www.newscientist.com/article/mg14018983.500-evolutions-neglected-superstars-there-is-nothing-glamorous-about-fleas-flukes-or-intestinal-worms-so-why-are-they-suddenly-attracting-so-much-attention.html
and here: http://discovermagazine.com/photos/04-zombie-animals-and-the-parasites-that-control-them
The original zombie ant study (online version of the paper contains a video):
Andersen, Sandra B., et al. (2009) The Life of a Dead Ant: The Expression of an Adaptive Extended Phenotype. The American Naturalist: 174(3), 424-433. (DOI: 10.1086/603640)
The new study, and because it is published in PLoS ONE it is free access (yay!):
Evans, Harry C., Simon L. Elliot, and David P. Hughes. (2011) Hidden Diversity Behind the Zombie-Ant Fungus Ophiocordyceps unilateralis: Four New Species Described from Carpenter Ants in Minas Gerais, Brazil. PLoS ONE: 6(3), e17024. (DOI:10.1371/journal.pone.0017024)
Online stories on this paper:
"(An) armoured lobopodian with ten pairs of appendages. Trunk region with nine segments, bearing rows of transverse annulations each with some tubercles. Each region possesses a pair of robust and sclerotized spiny appendages with primary articulation. Anterior is extended, probably forming a proboscis. Posterior region bears a protrusion."
That's the description of a new species found in China and described in the journal Nature last week. The species name is Diania cactiformis, the genus name referring to the Chinese province of Yunnan and the species epithet refering to it's cactus shape. Since, it has garnered the nickname the "walking cactus." It belongs to the group Lobopodia, a now extinct group consisting of small, segmented animals dating back to the early Cambrian. The dorsal armored or sclerotized plates are characteristic of this group. This group of organisms resembles velvet worms (Onychophorans) which are terrestrial worms with legs.
The new species was nicknamed the "walking cactus" because of its many appendages and spiny appearance. The specimen dates from around 500 million years ago, is about 6 centimeters (2.4 inches) long, and has the long worm-like body characteristic of lobopodians. What makes this creature unique is its hardened, jointed legs. These joints are important because they provide a link between lobopodians and arthorpods. Sure missing links are always great to find, but in this case what makes this link so significant? Well, the group Arthropoda contains more than 80% of all known living animal species, we're talking all insects, crustaceans, etc. This newly described link gives insight into how this group evolved. For example, the hardened surfaces of the legs of D. cactiformis imply that arthropods developed hardened limbs before hardened bodies, effectively the first step in evolving the body plan from soft-bodied to an articulated exoskeleton.
The Field Museum in Chicago have imagined it to move something like this:
Read more and see pictures in the paper:
Liu, Jianni, et al. (2011) An armoured Cambrian lobopodian from China with arthopod-like appendages. Nature: 470, 526-530. (DOI: 10.1038/nature09704)
And some story links: