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

A |     二次创业，塞罕坝续写绿色传奇（全面推进美丽中国建设）

塞罕坝机械林场。    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。孙 阁摄

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图三2021年8月23日，习近平总书记考察塞罕坝机械林场时强调，“塞罕坝林场建设史是一部可歌可泣的艰苦奋斗史。你们用实际行动铸就了牢记使命、艰苦创业、绿色发展的塞罕坝精神，这对全国生态文明建设具有重要示范意义。抓生态文明建设，既要靠物质，也要靠精神。要传承好塞罕坝精神，深刻理解和落实生态文明理念，再接再厉、二次创业，在实现第二个百年奋斗目标新征程上再建功立业。”新一代塞罕坝务林人，正以牢记使命的定力守护绿色，以艰苦创业的劲头拓展绿色，以绿色发展的智慧经营绿色，在二次创业的征程上写下新的答卷。——编 者“卫星热点监测平均4分多钟扫描一次”8月，塞罕坝。站在山顶远眺，层层叠叠的绿树覆盖着峰峦沟壑，仿佛一幅铺展在大地上的油画。

B | 塞罕坝机械林场护林防火（安全生产）办公室主任时辰（见图一）的一天，从查看监控屏幕开始。时辰是不折不扣的“林三代”，他的爷爷时国成，1962年作为第一代务林人来到塞罕坝。在时辰的记忆里，爷爷总是笑着回忆当年一人“身兼多职”，既做护林员，又做施工员，还兼任核算员和炊事员。2014年，时辰大学毕业后也回到林场。“走在树下就有使命感，要把这片林海守护好。”时辰说。但守护的方式，已与祖辈天差地别。林场最高处的“望海楼”上，新安装的林火视频监控系统利用“双光摄像头”监测可见光和热成像，可清晰覆盖半径15公里的区域。太空中，12颗人造卫星实时巡护；林区内，223套监控设备布设在沟谷、高点与路口。

C | 无人机不时掠过树梢，红外探火雷达24小时扫描……“天空地”一体化防火预警监测体系全面覆盖。“卫星热点监测平均4分多钟扫描一次，假如出现火点，会自动标识方位。”时辰介绍。不仅如此，每年4月，坝上积雪初融，时辰便带队踏查每个地块，开展营林抚育、病虫害防治等工作。林场采用化学、物理、生物综合治理，虫害无公害防治率达95%以上，鼠害无公害防治率达100%，有害生物成灾率控制在3‰以下。林火监测覆盖率实现100%。

D | 自建场以来，塞罕坝持续保持无火灾记录。

E | “老一辈凭韧劲造出百万亩林海，我们接过接力棒，就要踏踏实实做好每件事。”时辰说。“扩绿不光是多种树，更是种好树”清晨5点，塞罕坝机械林场千层板分场场长张磊（见图二）出现在马蹄坑营林区边缘山坡上，观察新造林长势。这片林地是塞罕坝百万亩林海的起源地——60多年前，第一代建设者在此打响“马蹄坑大会战”，创下造林成活率超90%的奇迹。如今，它再次成为二次创业的试验田。向石质荒山要绿色，是二次创业中最硬的仗。石质阳坡——坡度30度以上、土壤贫瘠、岩石裸露——被公认为造林界的世界级难题。“石头山上种树，难度不亚于沙漠造林。”张磊说。不服输的塞罕坝人，发扬艰苦创业精神，在屡败屡战中摸索出客土、壮苗、覆膜、覆土的技术规范，硬是把不可能变成可能：挖70厘米见方大坑，再挖30厘米小坑，从别处背熟土填入，把苗圃培育了两三年的容器苗背上山栽下，覆土压实后覆膜保墒，最后加装防护栏……机器上不了那么陡的坡，怎么办？“人背，或者马驮、骡驮，一趟一趟爬。

F | ”张磊说。攻坚造林，10.6万亩石质山地全部绿化，成活率、保存率分别达98.9%、92.2%。

G | 目前，林场有林地面积115.1万亩，森林覆盖率达82%。“扩绿不光是多种树，更是种好树。”森林中，张磊拨开草丛，蹲在一棵西伯利亚红松旁说道：“去年引进的，顺利越冬，今年抽了新枝。”“树种单一，一旦发生病虫害或气候异常，风险很大。

H | ”张磊解释，像这种采用不同树龄、针叶阔叶混交的近自然种植模式，可大幅提升生态系统多样性与稳定性。

I | “十四五”时期，林场完成营造林57.05万亩，累计新增混交林面积6.2万亩，混交林占比从21.4%提升至26.9%。森林多样性提升，带来生物多样性显著增加。最新科考发现，野生动植物、大型真菌等增加858种。“把这片林子管好、护好、发展好，碳汇自然就有了”塞罕坝机械林场营林科科长常伟强（见图三）站在羊场营林区高坡上，指着一片新造的混交林说：“这片林子，就是碳汇。”近年来，省相继出台降碳产品价值实现等支持措施，推动“碳库”变“钱库”。2022年，塞罕坝机械林场开发省森林固碳生态产品33万亩，核证碳汇量225.1万吨。

J | 2024年，全国温室气体自愿减排交易市场重启。塞罕坝机械林场签署全国温室气体自愿减排项目开发和减排量交易合规倡议，并于同年完成首笔交易。“十四五”时期，塞罕坝机械林场已累计销售林业碳汇35.7万吨，实现价值转化1178万元。常伟强介绍，碳汇的核定有一套复杂的计算方法——依据造林面积、树种、造林密度等参数测定固碳量，“把这片林子管好、护好、发展好，碳汇自然就有了。”如今，塞罕坝的“绿色”种子，正源源不断播撒向更广阔的土地。塞罕坝正在建设省级林木种质资源库，围绕坝上高寒耐寒的乡土树种划定保护区域。林场培育的华北落叶松、樟子松等苗木，成为“三北”地区防风固沙、水源涵养的主力树种。塞罕坝的苗木、技术和人才，还有力支援了雄安新区“千年秀林”建设。5年间，塞罕坝人用行动作答：石质荒山全部披绿，混交林面积突破29万亩，林火监测全覆盖，碳汇交易实现新突破。林场先后获评全国脱贫攻坚楷模、联合国“地球卫士奖”“土地生命奖”等。从“一棵松”到“一片海”，从“人防”到“智防”，从“砍树”到“卖碳”——塞罕坝的二次创业，正在新一代务林人手中，续写新的绿色奇迹。

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Published on:11:10:27