An international team of astronomers has found that four Earth-sized planets orbit the nearest Sun-like star, Tau Ceti, which lies 12 light years away and is visible to the naked eye. These planets have masses as low as 1.7 Earth mass, making them among the smallest planets ever to be detected around G-type stars near our Solar System. Two are super-Earths located in the habitable zone, meaning they could support liquid surface water.
The planets were detected by observing tiny wobbles in the movement of Tau Ceti. This required techniques sensitive enough to detect variations in the movement of the star as small as 30 centimetres (12 inches) per second.
"We are now finally crossing a threshold where, through very sophisticated modelling of large combined data sets, we can disentangle the noise due to stellar surface activity from very tiny signals generated by the gravitational tugs of Earth-sized orbiting planets," said the study co-author, Steven Vogt, Professor of Astronomy and Astrophysics at the University of California, Santa Cruz.
Illustration courtesy of Fabo Feng
According to lead author Fabo Feng at the University of Hertfordshire, UK, researchers are now tantalisingly close to the 10-centimetre-per-second limit required for detecting Earth analogues: "Our detection of such weak wobbles is a milestone in the search for Earth analogues and the understanding of the Earth's habitability through comparison with these analogues," said Feng. "We have introduced new methods to remove the noise in the data in order to reveal the weak planetary signals."
As shown in the diagram above, the outer two planets around Tau Ceti are likely to be candidate habitable worlds – although a massive debris disc around the star probably reduces their habitability, due to intensive bombardment by asteroids and comets.
The same team also investigated Tau Ceti in 2013, when co-author Mikko Tuomi from the University of Hertfordshire led an effort in developing data analysis techniques and using the star as a benchmark case: "We came up with an ingenious way of telling the difference between signals caused by planets and those caused by a star's activity," he explains. "We realised that we could see how a star's activity differed at different wavelengths and use that information to separate this activity from signals of planets."
The team painstakingly improved the sensitivity of their method and were able to rule out two signals they had identified in 2013 as planets: "But no matter how we look at the star, there seem to be at least four rocky planets orbiting it," Tuomi says. "We are slowly learning to tell the difference between wobbles caused by planets, and those caused by stellar active surface. This enabled us to essentially verify the existence of the two outer, potentially habitable planets in the system."
Sun-like stars are thought to be the best targets in the search for habitable Earth-like planets, due to their similarity to our Sun. Unlike more common smaller stars, such as the red dwarf stars Proxima Centauri and Trappist-1, they are not so faint that planets would be tidally locked, showing the same side to the star at all times. Tau Ceti is very similar to the Sun in its size and brightness, and both stars host multi-planet systems.
A paper on these new findings was accepted for publication in the peer-reviewed Astronomical Journal and is available online. The data was obtained by using the HARPS spectrograph (European Southern Observatory, Chile) and Keck-HIRES (W. M. Keck Observatory, Mauna Kea, Hawaii).
The Sun (left) and Tau Ceti (right). Both are G-type stars.
Credit: R.J. Hall [CC-BY-SA-3.0], via Wikimedia Commons
Astronomers have announced the surprise detection of a large rock, possibly up to 93 m (305 ft) in size, which hurtled past Earth last week.
Images courtesy of the Minor Planet Center. The green line indicates the object's apparent motion relative to the Earth, and the bright green dots are the object's location at approximately one hour intervals. The Moon's orbit is grey. The blue arrow points in the direction of Earth's motion and the yellow arrow points toward the Sun.
At just one-third the Earth-moon distance, or 76,448 mi (123,031 km), the asteroid now named 2017 OO1 came within a whisker – in astronomical terms – of colliding with our planet. The object flew by at 23,200 mph (10.3 km/s) on 21st July at 03:33 UTC. However, it was only detected by the ATLAS-MLO telescope in Hawaii on 23rd July, two days after its closest approach. The object, with a very faint magnitude of 17.9, is very dark and likely to have a non-reflective surface that made it very difficult to spot.
While asteroids of this size are too small to cause an extinction-level event, their speed and kinetic energy can still do enormous damage. Inputting the figures into an impact calculator shows that 2017 OO1 would enter our atmosphere with a force equivalent to 11.6 megatons of TNT. Breaking up at an altitude of 29.3 mi (47.1 km), it would hit the ground at 13,400 mph (6 km/s), with a blast of 3.32 megatons. That is over 200 times more powerful than the Hiroshima bomb of 1945.
If on land, the impactor would produce a crater with radius of 2,132 ft (650 m) and depth of 820 ft (250 m). All buildings and most bridges within a radius of 1.6 mi (2.5 km) would be destroyed, with glass shattering up to 31 mi (50 km) away. If landing in the ocean, a megatsunami would be produced with waves of up to 500 ft (150 m) within a radius of 1 mile (1.6 km). These would decrease rapidly in height, to 62 ft (19 m) at a distance of 6.2 mi (10 km) but would have enough momentum to continue at 7 ft (2 m) height for over 62 mi (100 km).
We may sometimes joke and make light of such catastrophes – they are a popular staple of science fiction. But asteroids can also be very real, as the Chelyabinsk event of 2013 made clear. That involved a rock that was much smaller than 2017 OO1, with only 1/7th as much energy. It is surely only a matter of time before such an incident occurs again somewhere in the world; perhaps in a major urban region. Indeed, the B612 Foundation showed in a presentation that asteroid impacts are more common than previously thought. Over 10,000 near-Earth objects have been discovered to date, of which nearly ten percent are larger than 3,280 ft (1,000 m). There are possibly ten times as many still waiting to be found within our Solar System.
In related news, NASA will be using its network of observatories and scientists to track and characterise a small asteroid known as TC4 that will pass close to Earth on 12th October. Yesterday the agency provided more details of the initiative, which aims to test its worldwide asteroid detection and tracking abilities – assessing the capability of scientists to work together in response to a potential real asteroid threat.
"Asteroids," Neil deGrasse Tyson once tweeted, "are nature's way of asking: 'How's that space program coming along?'"
Astrophysicists report that tardigrade micro-animals may be one of the most resilient lifeforms on Earth, able to withstand global mass extinctions due to astrophysical events, such as supernovae, gamma-ray bursts, large asteroid impacts, and passing-by stars.
The world's most indestructible species, the tardigrade – an eight-legged micro-animal, also known as the water bear – will survive until the Sun dies, according to a new collaboration between Harvard and Oxford University.
Although much attention has been given to the potential impact of astrophysical events on human life, very little has been published about what it would take to kill the tardigrade and wipe out life on our planet. The new research implies that life will persist for as long as the Sun continues to shine. It also reveals that once life emerges, it is surprisingly resilient and difficult to destroy, boosting the odds of life on other planets.
The study, published in Scientific Reports, shows that the tiny creatures will survive the risk of extinction from all astrophysical catastrophes, and be around for billions of years – far longer than the human race.
Tardigrades are the toughest, most resilient animals on Earth – able to survive for up to 30 years without food or water, and endure temperature extremes of up to 150 degrees Celsius, the deep sea and even the frozen vacuum of space. The water-dwelling micro animal is only 0.5mm (0.02 inches) in size, but can live for up to 60 years. Researchers from the Universities of Oxford and Harvard concluded that they could most likely survive all astrophysical calamities.
Three potential events were considered as part of their research:
There are only a dozen known asteroids and dwarf planets with enough mass to boil the oceans (2x10^18 kg), these include Vesta (2x10^20 kg) and Pluto (10^22 kg). However, none of these objects will intersect the Earth's orbit and pose a threat to tardigrades.
In order to boil the oceans, an exploding star would need to be 0.14 light years away. The closest star to the Sun is 4.2 light years away and the probability of a massive star exploding close enough to Earth to kill all lifeforms on it, within the Sun's lifetime, is negligible.
Gamma-ray bursts are brighter and rarer than supernovae. Much like supernovas, gamma-ray bursts are too far away from Earth to be considered a viable threat. To boil the world's oceans, the burst would need to be within 40 light years, and the likelihood of a burst occurring so close is again, minor.
Gamma-ray burst. Credit: NASA
"Without our technology protecting us, humans are a very sensitive species," said Dr Rafael Alves Batista, Co-author and Post-Doctoral Research Associate in the Department of Physics at Oxford University. "Subtle changes in our environment impact us dramatically. There are many more resilient species on Earth. Life on this planet can continue long after humans are gone. Tardigrades are as close to indestructible as it gets on Earth, but it is possible that there are other resilient species examples elsewhere in the universe. In this context, there is a real case for looking for life on Mars and in other areas of the Solar System in general. If Tardigrades are Earth's most resilient species, who knows what else is out there?"
"A lot of previous work has focused on 'doomsday' scenarios on Earth – astrophysical events like supernovae that could wipe out the human race," explains Dr David Sloan, co-author from the same department at Oxford University. "Our study instead considered the hardiest species – the tardigrade. As we are now entering a stage of astronomy where we have seen exoplanets and are hoping to soon perform spectroscopy, looking for signatures of life, we should try to see just how fragile this hardiest life is. To our surprise we found that although nearby supernovae or large asteroid impacts would be catastrophic for people, tardigrades could be unaffected. Therefore it seems that life, once it gets going, is hard to wipe out entirely. Huge numbers of species, or even entire genera may become extinct, but life as a whole will go on."
In highlighting the resilience of life in general, the research broadens the scope of life beyond Earth, within and beyond the Solar System.
"It is difficult to eliminate all forms of life from a habitable planet," explains Professor Abraham Loeb, co-author and chair of the Astronomy department at Harvard University. "The history of Mars indicates that it once had an atmosphere that could have supported life, albeit under extreme conditions. Organisms with similar tolerances to radiation and temperature as tardigrades could survive long-term below the surface in these conditions. The subsurface oceans that are believed to exist on Europa and Enceladus would have conditions similar to the deep oceans of Earth where tardigrades are found, volcanic vents providing heat in an environment devoid of light. The discovery of extremophiles in such locations would be a significant step forward in bracketing the range of conditions for life to exist on planets around other stars."
Luxembourg yesterday passed a draft law on the exploration and use of space resources. The Grand Duchy is thus the first European country to offer a legal framework ensuring that private operators can be confident about their rights on resources they extract in space.
The new law – approved by a majority of 55 votes against two – will come into force on 1st August 2017. Its first article provides that space resources are capable of being owned. It also establishes the procedures for authorising and supervising space exploration missions.
This legal and regulatory framework is a key part of the SpaceResources.lu initiative, whose goal is to support the long-term economic development of new, innovative activities in the space industry. Within this strategy, Luxembourg has already begun to support research and development projects of leading players in the space mining industry that have set up their European operations in Luxembourg. For example, US firms Deep Space Industries and Planetary Resources both have subsidiaries there now; the latter finalised a 25 million euro agreement last year to accelerate the company's technical advancements, with the aim of launching a first commercial asteroid mission by 2020.
It is hoped that the SpaceResources.lu initiative can build on the experience Luxembourg has gained in sectors that are closely related to space mining, and in particular on its strong track record in the satellite sector. In 1985, a public-private partnership effort launched Société Européenne des Satellites, today known as the largest global satellite operator SES with its headquarters in Luxembourg. This now controls more than 50 satellites.
Deputy Prime Minister, Étienne Schneider, said: "Luxembourg is the first adopter in Europe of a legal and regulatory framework recognising that space resources are capable of being owned by private companies. The Grand Duchy thus reinforces its position as a European hub for the exploration and use of space resources. The legal framework is part of the expertise ecosystem and the business-friendly, innovation-nurturing environment that Luxembourg is offering to space industry companies. By adopting almost unanimously the respective draft law, the Luxembourg Parliament confirmed the strong political cross-party and national commitment to the SpaceResources.lu initiative."
“Luxembourg continues to be a strong partner and a global leader,” said Chris Lewicki, Planetary Resources CEO. “They are genuinely forward thinking, have a proven record in the satellite industry, and are making their mark on the space mining industry. The passage of this law is further proof of that.”
Alongside steps taken on the national level within the SpaceResources.lu initiative, Luxembourg continues to promote international cooperation in order to make progress on a future governance scheme and a global regulatory framework for space mining. In line with this, the Grand Duchy recently signed a joint statement with the European Space Agency (ESA) on future activities concerning missions to asteroids, related technologies and space resources exploration and utilisation. Luxembourg and the ESA agreed on the opportunity to further study technical and scientific aspects of space resources.
In April, a report by Goldman Sachs revealed that asteroid mining is “more realistic than perceived” – thanks to the falling costs of access to space – and is likely to bring enormous rewards to companies able to develop the necessary technologies for extraction. A single 500-metre-wide asteroid could contain nearly 175 times the global output of platinum.
The discovery of the smallest star able to sustain nuclear fusion has been announced; its diameter is just slightly larger than that of Saturn.
Images and text credit: University of Cambridge, Wikimedia Creative Commons license, Attribution 4.0 International (CC BY 4.0)
The smallest star yet measured has been discovered by a team of astronomers led by the University of Cambridge. With a diameter just slightly larger than that of Saturn, the gravitational pull at its stellar surface is about 300 times stronger than what humans feel on Earth. With just enough mass to enable the fusion of hydrogen nuclei into helium, it is likely as small as stars can possibly become. If it were any smaller, the pressure at its centre would no longer be sufficient to enable this process to take place. Hydrogen fusion is also what powers the Sun, and scientists are attempting to replicate it as a powerful energy source here on Earth.
Very small and dim stars like this one are also the best possible candidates for detecting Earth-sized planets with liquid water on their surfaces, such as TRAPPIST-1, an ultracool dwarf surrounded by seven temperate Earth-sized worlds.
The newly-found star – EBLM J0555-57Ab – is about 600 light years away in the constellation Pictor, in the direction of the Large Magellanic Cloud. It is part of a binary system, and was identified as it passed in front of its much larger companion, a method normally used to detect planets, not stars.
EBLM J0555-57 binary system, imaged by ESO’s La Silla Observatory. Credit: Alexander von Boetticher et al.
“Our discovery reveals how small stars can be,” said Alexander Boetticher, the lead author of the study, and a Master’s student at Cambridge’s Cavendish Laboratory and Institute of Astronomy. “Had this star formed with only a slightly lower mass, the fusion reaction of hydrogen in its core could not be sustained, and the star would instead have transformed into a brown dwarf.”
EBLM J0555-57Ab was identified using data from the Wide Angle Search for Planets (WASP), an experiment run by the Universities of Keele, Warwick, Leicester and St Andrews. It was found to circle its primary star companion with an orbital period of just 7.8 days, and has a mass of 85 Jupiters.
“This star is smaller, and likely colder than many of the gas giant exoplanets that have so far been identified,” said Boetticher. “While a fascinating feature of stellar physics, it is often harder to measure the size of such dim low-mass stars than for many of the larger planets. Thankfully, we can find these small stars with planet-hunting equipment, when they orbit a larger host star in a binary system. It might sound incredible, but finding a star can at times be harder than finding a planet.”
Despite being the most numerous stars in the Universe, stars with sizes and masses less than 20% that of our Sun are poorly understood, since they are difficult to detect. The EBLM project, which identified the star in this study, aims to plug that gap in knowledge: “Thanks to the EBLM project, we will achieve a far greater understanding of the planets orbiting the most common stars that exist; planets like those orbiting TRAPPIST-1,” said co-author Prof. Didier Queloz of Cambridge's Cavendish Laboratory. The team's work is published in the journal Astronomy & Astrophysics.
The European Space Agency (ESA) has confirmed the Laser Interferometer Space Antenna (LISA) as the third large-class mission in its future science programme, with launch planned for 2034.
A trio of satellites to detect gravitational waves has been selected as the third large-class (L3) mission in ESA's Science programme. In terms of its area and dimensions covered, the Laser Interferometer Space Antenna (LISA) will be the largest man-made structure ever put into space – with each "side" of its triangle stretching across millions of kilometres – forming a giant observatory to probe the Dark Side of the Universe.
In 2013, the "gravitational universe" was chosen as the theme for a future ESA mission. This would be designed to search for ripples in the fabric of space-time created by celestial objects with extremely strong gravity, such as pairs of merging black holes.
Gravitational waves were predicted a century ago by Albert Einstein's general theory of relativity, but remained elusive until very recently, when the first direct detection was made by the ground-based Laser Interferometer Gravitational-Wave Observatory (LIGO). That signal, announced in February 2016, was triggered by the merging of two black holes some 1.3 billion light-years away.
Since then, two more events have been detected and a follow-up study, LISA Pathfinder, has demonstrated that observations can be made in space – not just with ground-based instruments. This precursor mission will conclude on 30th June, after sixteen months of science operations, which have tested key technologies needed for the more advanced LISA in the 2030s.
Space-based operations will provide major advantages:
• no need to create an artificial vacuum, since the vacuum of space is free and better than anything that can be simulated in a lab;
• no interference from seismic noise, such as earthquakes or plate tectonics, passing vehicles and other human activity;
• no limitations in size for the observatory arms, which would otherwise be restricted by the curvature of the Earth.
To detect and measure gravitational waves from distant astronomical sources, a phenomenal level of sensitivity is required. Using laser interferometry over its trio of 2.5 million kilometre arms, LISA will track relative displacements with a resolution of 20 picometres – 1/50 billionth of a metre – less than the width of a helium atom. It will look for ripples in space-time with periods ranging from a few minutes to a few hours. Several thousand objects are expected to be resolved within the first year of operation.
In addition to studying black holes and compact binaries, LISA will probe the expansion of the universe and the gravitational wave background created during the early universe. It will also look for currently unknown (and unmodelled) sources of gravitational waves. History in astrophysics has shown that whenever a new frequency range/medium of detection is available, new and unexpected sources show up. This may, for example, include kinks and cusps in cosmic strings.
Following its selection, LISA will now enter a more detailed phase of design and costing, before construction begins. Its launch is expected during 2034 and the mission lifetime is four years – but the spacecraft will have enough power and orbital stability to potentially last until 2044.
Chinese scientists report the transmission of entangled photons between suborbital space and Earth, using the satellite Micius. More satellites could follow in the near future, with plans for a European–Asian quantum-encrypted network by 2020, and a global network by 2030.
In a landmark study, Chinese scientists report the successful transmission of entangled photons between suborbital space and Earth. Furthermore, whereas the previous record for entanglement distance was 100 km (62 miles), here, transmission over more than 1,200 km (746 miles) was achieved.
The distribution of quantum entanglement, especially across vast distances, holds major implications for quantum teleportation and encryption networks. Yet, efforts to entangle quantum particles – essentially "linking" them together over long distances – have been limited to 100 km or less, mainly because the entanglement is lost as they are transmitted along optical fibres, or through open space on land.
One way to overcome this issue is to break the line of transmission into smaller segments and repeatedly swap, purify and store quantum information along the optical fibre. Another approach to achieving global quantum networks is by making use of lasers and satellite technologies. Using a Chinese satellite called Micius, launched last year and equipped with specialised quantum tools, Juan Yin et al. demonstrated the latter feat. The Micius satellite was used to communicate with three ground stations across China, each up to 1,200 km apart.
The separation between the orbiting satellite and these ground stations varied from 500 to 2,000 km. A laser beam on the satellite was subjected to a beam splitter, which gave the beam two distinct polarised states. One of the spilt beams was used for transmission of entangled photons, while the other was used for photon receipt. In this way, entangled photons were received at the separate ground stations.
"It's a huge, major achievement," Thomas Jennewein, physicist at the University of Waterloo in Canada, told Science. "They started with this bold idea and managed to do it."
"The Chinese experiment is quite a remarkable technological achievement," said Artur Ekert, a professor of quantum physics at the University of Oxford, in an interview with Live Science. "When I proposed the entangled-based quantum key distribution back in 1991 when I was a student in Oxford, I did not expect it to be elevated to such heights."
One of the many challenges faced by the team was keeping the beams of photons focused precisely on the ground stations as the satellite hurtled through space at nearly 8 kilometres per second.
Quantum encryption, if successfully developed, could revolutionise communications. Information sent via this method would, in theory, be absolutely secure and practically impossible for hackers to intercept. If two people shared an encrypted quantum message, a third person would be unable to access it without changing the information in an unpredictable way. Further satellite tests are planned by China in the near future, with potential for a European–Asian quantum-encrypted network by 2020, and a global network by 2030.