Overall, this is a very disturbing report. There has been a longstanding debate among scientists as to whether sperm counts have decreased or not. But what’s different about this study is the quality of the analysis. It was done in a systematic manner, accounting for several of the problems that had affected previous studies, such as the method used to count sperm and comparing studies performed sometimes decades apart. As such, most experts agree that the data presented is of a high quality and that the conclusions, although alarming, are reliable.
So what is going on? There has been concern for a number of years about an increase in abnormalities in male reproductive health, such as testicular cancer. The decline in sperm counts is consistent with these increases and this adds weight to the concept that male reproductive health is under attack and is declining rapidly.
In fact, if the data on sperm counts is extrapolated to its logical conclusion, men will have little or no reproductive capacity from 2060 onwards. The most rational explanation for the decline in male reproductive health is the changes in the environment. Current research suggests that the male foetus is particularly susceptible to exposure to pollutants and so changes that occur early in foetal life can have a very significant effect on the adult.
The simple answer is that we need much more research to find out why this decline in sperm count is happening. We cannot be complacent about the potential negative effect on fertility and must now urgently rally to substantially increase the research effort into male reproductive health.
Also, although the prevailing evidence shows a decline in reproductive health, not all studies show this; there are some geographical differences. It will be critical to determine what the key differences between geographical regions are – such as genetic differences and exposure to specific pollutants – so we can then examine treatment strategies to limit these negative effects.
If it’s the foetus that is mainly affected, what can the adult man do? Even in adults, exposure to chemicals, such as bisphenol A, which are thought to affect fertility, can have a negative effect, so men should limit their exposure to toxic chemicals. This includes stopping cigarette smoking. Also, a healthy lifestyle is very important as there is a known link between obesity and reduced sperm count.
By Chris Barratt, Professor of Reproductive Medicine, University of Dundee
This article was originally published on The Conversation. Read the original article.
Prior to launch, Mayak was just 30 centimetres long; such a tiny satellite would normally be difficult to see unaided. But Mayak is designed to unfurl a three-metre highly reflective sheet that can beam sunlight down to Earth.
Will Mayak be the brightest object in the night sky apart from the Moon? Will our night sky be flooded by artificial stars? Is this the start of advertising in space?
Or can we relax and enjoy this new visitor to the night skies?
A bugbear of astronomers, both professional and amateur, is light pollution. In cities and towns across the world, faint stars are hidden from view because the atmosphere reflects artificial light back at us.
Light pollution hinders our view of the night sky.
While we don’t think of the Moon as a source of light pollution, it also makes the night sky brighter. When there’s a full Moon it is far more difficult to see the glow of the Milky Way stretching across the heavens.
Although Mayak weighs just a few kilograms and is currently more than 500km above Earth, it could end up being very bright indeed.
Mayak is designed to unfurl a reflective pyramid, with each side of the pyramid having a surface area of four square metres. (At the time of writing, it’s unclear whether the pyramid has been unfurled.)
If the sides of Mayak’s pyramid were perfectly flat mirrors, then Mayak could be a tenth as bright as the full Moon. That’s bright enough to cast shadows here on Earth on a dark night.
But photos make it clear that Mayak’s reflectors were never intended to be perfectly flat mirrors, so it won’t be that bright.
Mayak’s reflectors may only illuminate regions of Earth’s surface that are tens of kilometres across. As Mayak is moving at more than seven kilometres every second, it may appear as a bright star only briefly.
There are plans to improve Mayak’s visibility by setting it tumbling, so that it flashes as it moves across the sky, although these flashes may not seem spectacularly bright.
Highly reflective satellites have been launched before, including NASA’s inflatable PAGEOS.
Given Mayak’s fleeting passage, it is not going to produce much light pollution. Even if Mayak reflected light directly into a telescope, its rapid passage across the sky should reduce the chance of it damaging sensitive astronomical instruments. That said, I wouldn’t be happy if it spoiled one of my astronomical images.
Also, Mayak is not the first satellite to produce such fleeting “satellite flares”. The fleet of Iridium communication satellites has been orbiting Earth for two decades, and at any given location several such flares can be seen each week (they are sometimes mistaken for UFOs).
I personally enjoy seeing bright Iridium satellite flares. If you want to see some for yourself, you can look up predictions at Heavens Above.
The idea of advertising from space has been kicking around for decades. In 1956, a year before Sputnik, Arthur C. Clarke wrote of guerrilla advertising from the Moon in Watch this Space. In the 1990s Space Marketing Inc. proposed launching billboards into space.
The Mayak team includes employees of a Russian advertising agency, called 12, so is Mayak the beginning of advertising from space? To be blunt, no. And the ad agency says it does not want to move advertising to space, although it admits that others may be interested in that idea.
Besides, Mayak will be so small when viewed from Earth that it will look like a point of light.
A billboard in orbit just isn’t practical. Given what the unaided eye can see, an orbiting billboard would need pixels (roughly) 50 metres in size. That means a 100x100-pixel image would require a square billboard 5km high. Apart from the impractical size, such an enormous object would be a huge target for (and creator of) space junk.
While Mayak’s reflectors do gain attention (including media coverage), they are not intended to be billboards, but are a parachute (of sorts).
Satellites can remain in orbit for many years after they’ve stopped working, because at altitudes of hundreds of kilometres there’s very little atmospheric drag. For example, Vanguard 1, launched in 1958, is still orbiting the Earth.
Mayak’s practical purpose is to test a technology for reducing space junk, by dragging small satellites back to Earth. One can hasten the downfall of satellites by increasing their surface area. Mayak’s reflectors increase the satellite’s length from 0.3 metres (prior to launch) to 3 metres, greatly increasing the atmospheric drag it experiences.
If all goes well, Mayak will be dragged back to Earth in weeks, not years. Indeed, Mayak’s parachute won’t save it from destruction, but hasten its demise via reentry into the atmosphere. Then, very briefly, Mayak definitely will be the brightest shooting star in the sky.
Michael J. I. Brown, Associate professor, Monash University
This article was originally published on The Conversation. Read the original article.
How hot a planet gets depends primarily on how close it is to its host star – and on how hot that star burns. In our own solar system, Mercury is the closest planet to the sun at a mean distance of 57,910,000km. Temperatures on its dayside reach about 430°C, while the sun itself has a surface temperature of 5,500°C.
But stars more massive than the sun burn hotter. The star HD 195689 – also known as KELT-9 – is 2.5 times more massive than the sun and has a surface temperature of almost 10,000°C. Its planet, KELT-9b, is much closer to its host star than Mercury is to the sun.
Though we cannot measure the exact distance from afar, it circles its host star every 1.5 days (Mercury’s orbit takes 88 days). This results in a whopping 4300°C – which is hotter than many of the stars with a lower mass than our sun. The rocky planet Mercury would be a molten droplet of lava at this temperature. KELT-9b, however, is a Jupiter-type gas giant. It is shrivelling away as the molecules in its atmosphere are breaking down to their constituent atoms – and burning off.
At a temperature of just 50 degrees above absolute zero – -223°C – OGLE-2005-BLG-390Lb snatches the title of the coldest planet. At about 5.5 times the Earth’s mass it is likely to be a rocky planet too. Though not too distant from its host star at an orbit that would put it somewhere between Mars and Jupiter in our solar system, its host star is a low mass, cool star known as a red dwarf.
ESO, CC BY-SA
The planet is popularly referred to as Hoth in reference to an icy planet in the Star Wars franchise. Contrary to its fictional counterpart, however, it won’t be able to sustain much of an atmosphere (nor life, for that matter). This because most of its gases will be frozen solid – adding to the snow on the surface.
If a planet can be as hot as a star, what then makes the difference between stars and planets? Stars are so much more massive than planets that they are ignited by fusion processes as a result of the huge gravitational forces in their cores. Common stars like our sun burn by fusing hydrogen into helium. But there is a form of star called a brown dwarf, which are big enough to start some fusion processes but not large enough to sustain them. Planet DENIS-P J082303.1-491201 b with the equally unpronounceable alias 2MASS J08230313-4912012 b has 28.5 times the mass of Jupiter – making it the most massive planet listed in NASA’s exoplanet archive. It is so massive that it is debated whether it still is a planet (it would be a Jupiter-class gas giant) or whether it should actually be classified as a brown dwarf star. Ironically, its host star is a confirmed brown dwarf itself.
Just slightly larger than our moon and smaller than Mercury, Kepler-37b is the smallest exoplanet yet discovered. A rocky world, it is closer to its host star than Mercury is to the sun. That means the planet is too hot to support liquid water and hence life on its surface.
PSR B1620-26 b, at 12.7 billion years, is the oldest known planet. A gas giant 2.5 times the mass of Jupiter it has been seemingly around forever. Our universe at 13.8 billion years is only a billion years older.
NASA and G. Bacon (STScI)
PSR B1620-26 b has two host stars rotating around each other – and it has outseen the lives of both. These are a neutron star and a white dwarf, which are what is left when a star has burned all its fuel and exploded in a supernova. However, as it formed so early in the universe’s history, it probably doesn’t have enough of the heavy elements such as carbon and oxygen (which formed later) needed for life to evolve.
The planetary system V830 Tauri is only 2m years old. The host star has the same mass as our sun but twice the radius, which means it has not fully contracted into its final shape yet. The planet – a gas giant with three quarters the mass of Jupiter – is likewise probably still growing. That means it is acquiring more mass by frequently colliding with other planetary bodies like asteroids in its path – making it an unsafe place to be.
Because exoplanets are too far away for us to be able to observe any weather patterns we have to turn our eyes back to our solar system. If you have seen the giant swirling hurricanes photographed by the Juno spacecraft flying over Jupiter’s poles, the largest planet in our solar system is certainly a good contender. However, the title goes to Venus. A planet the same size of Earth, it is shrouded in clouds of sulfuric acid.
The atmosphere moves around the planet much faster than the planet rotates, with winds reaching hurricane speeds of 360km/h. Double-eyed cyclones are sustained above each pole. Its atmosphere is almost 100 times denser than Earth’s and made up of over 95% carbon dioxide. The resulting greenhouse effect creates hellish temperatures of at least 462°C on the surface, which is actually hotter than Mercury. Though bone-dry and hostile to life, the heat may explain why Venus has fewer volcanoes than Earth.
By Christian Schroeder, Lecturer in Environmental Science and Planetary Exploration, University of Stirling
This article was originally published on The Conversation. Read the original article.
