[ti:NASA Tests Earthquake-Seeking Balloons as Way to Study Venus] [by:www.51voa.com] [00:00.00]更多听力请访问51VOA.COM [00:00.04]U.S. space agency researchers successfully used [00:05.60]balloons to detect earthquakes in the California desert. [00:11.80]The experiment tested whether similar balloons [00:16.36]could be sent to Venus to study that planet's seismic activity. [00:22.96]NASA recently announced plans [00:26.36]to launch two future missions to Venus. [00:31.88]The NASA scientists got the chance [00:35.28]to carry out the test in July 2019, [00:40.12]when a series of powerful earthquakes [00:43.88]struck the area around Ridgecrest, California. [00:49.48]The main earthquake took place on July 4 [00:53.84]and had a magnitude of 6.4, [00:57.96]the United States Geological Survey reported in May. [01:04.48]Several other large quakes hit the area within days [01:09.36]and more than 10,000 aftershocks were reported [01:14.44]over the next six weeks. [01:18.04]The experiment involved four large sun-powered balloons [01:24.04]designed to fly at altitudes of 18 to 24 kilometers. [01:31.16]The team attached instruments to the balloons [01:35.80]that measure changes in air pressure. [01:39.84]The equipment is used to detect sound waves [01:44.72]that rise up from beneath the surface [01:48.64]during earthquakes and aftershocks. [01:52.96]The researchers say that by studying seismic wave activity [01:58.68]of a rocky planet, like Earth, they can learn more about [02:03.88]how that planet developed and about its current state. [02:10.24]Venus is also a rocky planet. [02:14.04]It is our closest neighbor in the solar system [02:18.00]and the second closest planet to the sun. [02:22.88]It is similar in structure to Earth, [02:25.92]but a little smaller. [02:28.64]But unlike Earth, Venus has an extremely hot surface temperature [02:35.04]and a very dense atmosphere. [02:38.52]Such conditions make it difficult for spacecraft [02:43.20]to survive in Venus' atmosphere or on its surface. [02:49.84]Scientists have long thought about the possibility [02:54.52]of studying seismic activity on Venus. [02:58.80]They want to learn more about how the planet [03:02.60]developed such extreme conditions. [03:06.88]The researchers, from NASA's Jet Propulsion Laboratory (JPL), [03:12.20]think they can send balloons like [03:14.92]the ones tested in California on a mission to Venus. [03:20.76]The experiment -- which also involved scientists [03:24.96]from the California Institute of Technology (Caltech) [03:28.64]--was recently described in a study [03:31.88]in Geophysical Research Letters. [03:36.84]Scientists from JPL and Caltech [03:41.04]have been developing their balloon-based method since 2016. [03:47.28]But the heavy earthquake activity in the California desert in July 2019 [03:54.84]gave them a good chance to test their equipment in the field. [04:01.08]Seismic energy from earthquakes is transmitted [04:06.48]into the atmosphere and produces sound waves. [04:12.08]These waves are detected by ground-based seismic stations. [04:17.60]But the JPL team reported it was able to detect, [04:23.40]for the first time, earthquake related seismic activity from its balloons. [04:31.76]One of the balloons detected seismic sound waves seconds [04:36.76]after a 4.2 magnitude aftershock [04:41.32]was confirmed by ground-based detection stations. [04:47.24]At the time, the balloon was about 4.8 kilometers above the Earth. [04:54.68]The researchers hope the balloons [04:57.68]will permit new studies of seismic activity on Venus [05:02.40]to provide information about the planet's interior. [05:08.16]For example, they say this method [05:11.52]could help them learn why the surface of Venus [05:15.40]stays hot enough to melt lead. [05:19.00]It may also lead to discoveries of liquid, [05:23.16]such as water or oil, on the planet. [05:27.84]Jennifer M. Jackson is a professor of mineral physics [05:33.56]at Caltech's Seismological Laboratory [05:37.36]who helped lead the research. [05:40.96]She said in a statement that much of our understanding [05:45.44]about Earth's interior comes from the study [05:49.72]of seismic activity happening deep inside the planet. [05:54.80]The method could also be possible with Venus. [06:00.24]"Observations of seismic activity... [06:04.12]would strengthen our understanding of rocky planets. [06:08.76]But Venus' extreme environment [06:12.64]requires us to investigate novel detection techniques." [06:18.60]The researchers say they plan to continue flying balloons [06:24.36]over seismically active areas to improve their ability [06:29.36]to identify seismic events over wide areas from the air. [06:36.76]They also plan to add more instruments [06:40.68]and fly more balloons at the same time. [06:45.60]This could permit them to identify where earthquakes happen [06:51.24]without the need for confirmation from ground stations. [06:56.72]I'm Bryan Lynn. 更多听力请访问51VOA.COM