极限挑战

'NASA ready to take whatever Universe throws at us'_我的网站

A |     Washington, Oct 12 (UNI) American space agency NASA says its recent attempt to deflect the path of an asteroid was successful, after its Dart probe struck an asteroid head-on.
Scientists have now confirmed the orbit of a 160m-wide space rock known as Dimorphos was altered when the Dart probe struck it head on last month.
Researchers came to the conclusion after making measurements using a range of space and Earth-based telescopes.
The mission was conceived to test a potential strategy to defend the Earth against threatening objects.
Dart's achievement proves such an idea would work, provided it was initiated early enough and the target wasn't overly massive.
"This mission shows that Nasa is trying to be ready for whatever the Universe throws at us," said agency administrator Bill Nelson.
"I believe that Nasa has proven that we are serious as a defender of the planet," he told reporters.
The space agency released a raft of data on Tuesday to support its assessment, including new pictures from the Hubble Space Telescope and from a small Italian spacecraft that stood off from the impact by about 50km (30 miles).
The Double Asteroid Redirection Test (Dart) took place some 11 million km (7 million miles) from Earth.
It saw the refrigerator-sized Nasa satellite drive straight into Dimorphos at 22,000km/h (14,000mph), destroying itself in the process.
The space rock orbits a much larger (780m wide; 2,550ft) object called Didymos. Before impact, the time taken for Dimorphos to make one circuit of its sibling was 11 hours and 55 minutes.
The telescope evidence now indicates this orbital period has been reduced to 11 hours and 23 minutes - a change of 32 minutes. This corresponds to Dimorphos moving closer into to Didymos by "tens of metres".
Nasa had defined a minimum successful period change of Dimorphos of 73 seconds or more. The results released on Tuesday show Dart surpassed this benchmark by more than 25 times.
"This is a 4 percent change in the orbital period of Dimorphos around Didymos. Dart just gave it a small nudge. But if you wanted to do this in the future, you'd want to do it years in advance," commented Nancy Chabot from the Johns Hopkins University Applied Physics Laboratory, which led the mission for Nasa.
"Warning time is really key here in order to enable this sort of asteroid deflection to be used in the future as part of a much larger planetary defence strategy."
Nasa's Dart programme scientist, Tom Statler, also had a word of caution about drawing too many conclusions from the experiment.
Asteroids came in many different guises, he said. Their compositions and constructions were diverse - something that was being emphasised every time a mission visited a new object.
"We should not be too eager to say one test on one asteroid tells us exactly how every other asteroid would behave in a similar situation," he stressed.
"But what we can do is use this test as an anchor point for our physics calculations in our simulations that tell us how different kinds of impacts in different situations should behave."
Four years from now, the European Space Agency (Esa) will have three spacecraft - collectively known as the Hera mission - at Didymos and Dimorphos to make follow-up studies.
UNI ING。

B |     今天（8月19日）是七夕佳节，你的出行计划安排好了吗？无论哪种选择，天气是否给力很关键。今天一早，阳光就已上线，杭州处于副高控制下的晴空区，预计今天杭州晴到多云为主，午后局部地区有阵雨或雷雨，雷雨时短时风雨较大，请大家注意防范局地可能出现的短时强风雨。此外，今年第18号台风“沙德尔”19日上午在西北太平洋洋面上生成，未来5天对我国海域无影响。今年第18号台风“沙德尔”生成最新路径预测今年第18号台风“沙德尔”（热带风暴级；英文名称：Saudel；名字来源：密克罗尼西亚；名称意义：密克罗尼西亚波纳佩岛（Pohnpei）传说中的将领“苏迪罗”信任的卫兵）19日上午在西北太平洋洋面上生成，中心附近最大风力有8级（18米/秒）。

C | 预计，“沙德尔”将以每小时15~20公里的速度向北偏西方向移动，强度逐渐增强，趋向琉球群岛以东洋面，未来5天对我国海域无影响。浙江雨水范围有所增大闷热感萦绕副高这位“虚胖”选手恐怕要撑不住了，季风槽已经按捺不住持续抢戏。接下来的天气舞台，雨水的“出镜率”增大，高温开始“摸鱼”。

D | 明后天雨水行程单：明天（周四）：明天的雨水排布，堪称“偏心眼”，沿海地区继续被“重点关照”，部分中到大雨打底，局部暴雨起步，个别站点甚至可能直接冲上大暴雨量级！而其他地区就“云淡风轻”多了，上午还能维持多云到阴的体面，中午前后起才陆续有阵雨或雷雨来“凑个热闹”。出门别犹豫，带伞还是“硬道理”。后天（周五）：雨水“低调”了不少，全省多云到阴，阵雨或雷雨偶尔来“串个门”。不过沿海地区依然不可掉以轻心，局部仍有暴雨出没的可能。周末及下周天气展望：22日-24日前期，季风槽环流继续“控场”，浙南和沿海地区依旧是降雨“主战场”，阵雨或雷雨频繁打卡。其他地区维持“多云+午后分散性阵雨或雷雨”的夏日天气配方。24日后期起，副高终于要“支棱”起来了！随着它势力加强，全省将转为多云天气，午后局部有分散性雷阵雨“偷袭”。不过副高一发力，部分地区气温将冲上35℃高温线，“焖蒸”模式可能再度回归！另外，我们要悄悄盯住西北太平洋，那边正有热带扰动（也就是台风的“胚胎”）在蠢蠢欲动。未来路径和强度还有很大不确定性，大家保持关注，有消息我们会第一时间“通风报信”！预计今天杭州晴到多云为主午后局部地区有阵雨或雷雨17日开始，退居海上多日的副热带高压（以下简称：副高）加强西伸，重新回到了我们的视野中。虽然随着副高的加强，代表副高的588线已完全将浙江纳入其控制范围，但由于处于加强初期，根基不稳，势力不强，让低层的水汽有了可乘之机。

E | 昨天（18日）下午，我市东部地区出现了明显的雷阵雨天气，最大累计雨量萧山义桥镇富春村54.0毫米（最大小时雨强53.0毫米），32个站风力大于6级，最大西湖转塘街道龙门坎村8级（17.7m/s）。今天一早，阳光就已上线，杭州处于副高控制下的晴空区，预计今天杭州晴到多云为主，午后局部地区有阵雨或雷雨，雷雨时短时风雨较大，请大家注意防范局地可能出现的短时强风雨。不过天气将很快迎来转折，今天后半夜到明天，随着台湾岛附近的低压系统逐渐北抬，杭州将受到其外围的东风气流的影响，转为多阵雨或雷雨的天气，同时后续的天气变化与低压系统的演变密切相关。

F | 目前预计20日-24日前期杭州都将有雨水影响，请大家及时关注最新的气象预报预警信息，提前调整行程，合理安排生产生活。目前来看，未来几天杭州雨水频繁，想要洗晒的朋友请抓紧今天的雨水空窗期，完成衣物、被褥的晾晒。后期受东风气流影响，多阵雨或雷雨，外出请随身携带雨具，同时要特别注意雷雨时短时强降水可能诱发的山体滑坡、泥石流、小流域山洪和城乡内涝等次生灾害。

G | 市区天气预报今天晴到多云，午后局部阴有阵雨或雷雨，雷雨时短时风雨较大；明天多云到阴有阵雨或雷雨，部分中雨；后天阴有阵雨或雷雨。今天偏东风3~4级阵风5级。明天白天最高气温31度（比今天低5度左右），明天早晨最低气温26度（与今天接近），明天平均相对湿度75%。（市气象台8月19日10时30分）昨日最高气温：34.7℃今日最低气温：26.2℃明天日出日落时间：日出05:29 日落18:36趋势预报： 20日（周四）：多云到阴有阵雨或雷雨，部分中雨，26~31℃，偏东风2~3级阵风5级；21日（周五）：阴有阵雨或雷雨，25~33℃，东南风2~3级阵风4~5级；22日（周六）：多云到阴有阵雨或雷雨，25~33℃，偏东风2~3级阵风4级；23日（周日）：多云到阴有阵雨或雷雨，26~32℃，东南风2~3级阵风4级;24日（周一）：多云，午后局部阴有阵雨或雷雨，25~32℃，东南风2~3级；25日（周二）：多云，午后局部阴有阵雨或雷雨，27~34℃，偏南风2~3级，阵风4级。杭州市气象台8月19日10时发布。

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