The Laser Interferometer Space Antenna (LISA) is launched
The Laser Interferometer Space Antenna (LISA) is a gravitational wave observatory launched by the European Space Agency.** This project is the third of three L-class (Large) missions in the "Cosmic Vision" programme which includes two other spacecraft – the Jupiter Icy Moon Explorer (JUICE) launched in 2022* and the Advanced Telescope for High ENergy Astrophysics (ATHENA) deployed in 2028.*
LISA is designed to sense gravitational waves – tiny ripples in the fabric of space-time – with extreme precision. Three spacecraft are placed in a triangular formation with 5 million kilometre sides, flying along an Earth-like heliocentric orbit. Laser interferometry is used to monitor fluctuations in the relative distances between them, with a resolution of just 20 picometres (20 trillionths of a metre, or smaller than a helium atom).*
To eliminate non-gravitational forces such as light pressure and solar wind on the test masses, each spacecraft is constructed as a zero-drag satellite and effectively "floats" around the masses, using capacitive sensing to determine their relative position, with ultra-precise thrusters to remain properly centred at all times.
Previous searches for gravitational waves in space were conducted for short periods by planetary missions with other primary objectives (such as Cassini–Huygens), using microwave Doppler tracking to monitor fluctuations in the Earth-spacecraft distance. By contrast, LISA is a dedicated mission using laser interferometry to achieve a much higher sensitivity. Other antennas had been operational on Earth, but their sensitivity at low frequencies was limited by the largest practical arm lengths, seismic noise, and interference from nearby moving masses.
Passing gravitational waves alternately squeeze and stretch objects by a tiny amount. These waves are caused by energetic events in the Universe, such as massive black holes merging at the centre of galaxies; black holes consuming small compact objects like neutron stars and white dwarfs; supernova star explosions; remnants from the very early phase of the Big Bang and possibly theoretical objects like cosmic strings and domain boundaries.
Since LISA is the first dedicated, space-based gravitational wave detector, the mission adds a whole new sense to our perception of the Universe – enabling astronomers to "hear" events in ways not possible before and revealing many important phenomena that were previously invisible.
phases out nuclear energy
Fukushima disaster in Japan, questions were raised about the long-term
viability of nuclear power. Switzerland was among the countries to abandon
this form of energy production, following public protests and a government
review in 2011. The country’s five existing reactors – supplying
about 40% of the country’s power – were allowed to continue
operating, but were not replaced at the end of their life span. The
last plant would be taken offline in 2034.*
A nuclear power
station with a cooling tower in Leibstadt, Switzerland.
Caribbean coral reefs are in danger of being wiped out
Often called "rainforests of the sea", coral reefs form some of the most diverse ecosystems on Earth. Historically, they have occupied less than 0.1% of the world's ocean surface – about half the area of France – yet provided a home for 25% of all marine species. Delivering a range of ecosystem services to tourism, fisheries and shoreline protection, the global economic value of coral reefs at one time was estimated at up to $375 billion each year.*
However, coral reefs are fragile ecosystems, partly because they are so sensitive to water temperature. In the early 21st century, they were under threat from climate change, oceanic acidification, blast fishing, cyanide fishing for aquarium fish, sunscreen use, overuse of reef resources, and harmful land-use practices; including urban and agricultural runoff and water pollution, harming reefs by encouraging excess algal growth.
The Caribbean – home to 9% of the world’s coral – saw a 50% decline between 1970 and 2012, leaving just one-sixth of the pre-industrial reef cover. According to a detailed analysis in 2014, virtually all of the remaining Caribbean coral reefs would disappear within 20 years, based on current trends.* Climate change had once been seen as the main culprit, lowering the pH level and causing bleaching. While ocean acidification was still a serious threat, new data suggested that a loss of parrotfish and sea urchin – the area’s two main grazers – was, in fact, the biggest driver of coral decline in this particular region.
For example, an order-of-magnitude increase in bulk shipping during the 1960s-70s introduced pathogens and invasive species near the Panama Canal that later spread to the Caribbean. An unidentified disease led to a mass mortality of the sea urchin in the 1980s, while extreme overfishing brought parrotfish to the brink of extinction in some regions. Loss of these species broke the delicate balance of coral ecosystems and enabled algae – on which they fed – to smother the reefs. Areas protected from overfishing, as well as other threats such as pollution, tourist activity and coastal development, were more resilient to pressures from climate change.
Some of the healthiest coral reefs, with high populations of grazing parrotfish, included the Flower Garden Banks National Marine Sanctuary in the northern Gulf of Mexico, Bermuda and Bonaire, all of which banned or restricted fishing practices that harmed the fish. Reefs where the parrotfish were not protected suffered tragic declines – such as Jamaica, the entire Florida Reef Tract from Miami to Key West, and the U.S. Virgin Islands.
Attempts were made in subsequent decades to protect these species across a wider area, and restore the balance between algae and coral using better management strategies. Although some of these efforts achieved modest success, short-term economic pressures and business interests tended to outweigh these concerns. The region as a whole remained under serious threat, and by 2034, Caribbean coral reefs have edged further towards complete collapse.*
Coral reef dead zones in the Caribbean. Credit: Catlin Seaview Survey