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Curiosity drills 6.4 cm (2.5 inch) holes on Mars. Comet harpoons have been proposed for future space probes. There are a number of ways in which we can penetrate the surface of terrestrial bodies, but I'm interested in what is the deepest we've gotten so far. As of April 2018, how deep have we gone (measured in vertical distance below surface)?

(To clarify, by "terrestrial" I mean to include all dwarf planets, comets, asteroids, moons, and terrestrial planets, unless by some marvelous exception it would stretch the definition too far--like a gas dwarf planet, were one to exist.)

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In July 2005, the Deep Impact mission released an impactor that excavated a crater, estimated to be 100 meters wide and 30 meters deep, into comet Tempel 1.

Tempel Alive with Light

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    $\begingroup$ On July 4th no less! $\endgroup$ – Mark Adler Apr 13 '18 at 5:59
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    $\begingroup$ More curiosity than quibbling, but do comets actually count as terrestrial bodies? $\endgroup$ – Mick O'Hea Apr 13 '18 at 10:43
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    $\begingroup$ @MickO'Hea: Only if they're primarily composed of silicate rocks, and thus "Earth-like" $\endgroup$ – Lightness Races in Orbit Apr 13 '18 at 11:51
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    $\begingroup$ @MickO'Hea Resolved the possible ambiguity in the question. $\endgroup$ – called2voyage Apr 13 '18 at 12:04
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Since the question is about terrestrial bodies, maybe the Deep Space 2 mission penetrating about 0.6 m (or 2 ft) into Mars was the deepest. At least that's what it was designed for, but we don't know if it reached that depth.

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  • $\begingroup$ They are sending a rover up for this soon for Mars. $\endgroup$ – Muze the good Troll. May 7 '18 at 3:41
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The non-comet runner up is probably the crater on the moon created by the impact of the Centaur upper stage from LCROSS. NASA estimated that at "approximately 28m (92 feet) in diameter by 5m (16 feet) deep".

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  • $\begingroup$ How does the LCROSS crater compare to the craters from the Saturn V upper stages? $\endgroup$ – Mark Apr 13 '18 at 22:28
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    $\begingroup$ Excellent point! According to lroc.sese.asu.edu/posts/60, "The LCROSS impactor (Centaur upper stage) is much smaller than the S-IVB and thus will make a smaller crater." I couldn't find any numbers on depth, but the S-IVB craters are 30-40m wide, so they're probably deeper too. $\endgroup$ – Simon Apr 14 '18 at 18:49
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https://ru.wikipedia.org/wiki/%D0%9B%D1%83%D0%BD%D0%B0-24

"Общая глубина бурения составила 225 сантиметров."

Translation: "Overall depth of drilling was 225 centimeters." That was Luna-24 in 1976, bringing back some Moon rocks.

From Gunter's Space Page Luna Ye-8-5M (Luna 23, 24):

Luna 24 was launched on 9 August 1976, entered lunar orbit on 14 August 1976 and successfully landed on 18 August 1976. The lander deployed its sample drill and pushed its drilling head about 2 meters into the lunar soil. The sample was transferred to the small return capsule, and after nearly a day on the Moon, Luna 24 lifted off successfully on 19 August 1976. The return capsule entered Earth's atmosphere and parachuted safely to the ground on 22 August 1976. The probe returned 170.1 grams of lunar soil.

From Russia Space Web's Luna-24: Last Moon digger:

As in previous soil-return missions, telemetry relayed information to ground control on the performance of the drilling mechanism and the process of loading of the samples into the return vehicle. (393) Data showed that Luna-24's drill reached a depth of two meters under a 30-degree angle toward the local vertical, penetrating 225 centimeters deep into the soil. (398) As a result, a 260-centimeter flexible tube with a diameter of 12 millimeters was partially filled with lunar regolith. The tube was then coiled in a spiral-like fashion on a special drum with a diameter of 80 millimeters, which in turn, was sealed inside the metal storage container of the reentry capsule.

enter image description here

The E8-5M spacecraft. Credit: NPO Lavochkin

Source

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As @Muze pointed out in a comment, the InSight Mars lander is the latest project of this kind on Mars. It begins digging this week and is designed to reach a depth of 5 m in approximately two months.

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EDIT: didn't realize terrestrial planets means only Mercury, Venus, Earth, Mars

EDIT2: wasn't aware the definition of 'surface' for a gas giant related to phase change, not to reaching some arbitrary pressure (e.g. 1 atm)

In 2012 Galileo was crashed into Jupiter and lasted 78 minutes, not clear how they define "penetrate the surface" or "depth" on a gas giant:

It entered the atmosphere of Jupiter at 30 miles per second (46km per second), the highest impact speed ever achieved by a man-made object. Amazingly, Jupiter’s dense atmosphere slowed the craft to 0.07 miles per second (0.12km per second) in just four minutes.

The probe’s heat shield, made of carbon phenolic, was able to withstand the 15,500°C ball of plasma caused by this sudden deceleration, producing light brighter than the Sun’s surface. It remained active for about 78 minutes as it passed through Jupiter’s atmosphere, losing more than half of its mass in the process before being crushed by the huge pressure.

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    $\begingroup$ My understanding is that Jupiter is not a terrestrial body. $\endgroup$ – Everyday Astronaut Apr 13 '18 at 21:17
  • $\begingroup$ @derwodamaso: my mistake $\endgroup$ – smci Apr 13 '18 at 21:21
  • $\begingroup$ Galileo burned in the atmosphere, I wouldn't say it penetrated at all. While it's not clearly defined I would say Jupiter has a surface--but it's far beyond our ability to reach at present. (I would define the point where it goes to metallic hydrogen as a surface.) $\endgroup$ – Loren Pechtel Apr 13 '18 at 23:19
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    $\begingroup$ Terrestrial bodies include terrestrial planets, but also some moons of Jupiter and Saturn, maybe even our moon. The OP's definition goes even further. Nonetheless, I find this answer interesting. $\endgroup$ – Everyday Astronaut Apr 14 '18 at 19:11
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    $\begingroup$ In planetary science a "surface" is usually considered a location where an essentially discontinuous change in state occurs, i.e. from gas to liquid or solid, or liquid to solid. At Jupiter (and Saturn) the transition to metallic hydrogen appears not to be that localized but instead is a zone hundreds or thousands of km in depth. As you go deeper into Jupiter the temperature rapidly increases, to ~15-20,000 K in the center, way above the critical temperatures of everything, even iron. There's no "surface", anywhere. $\endgroup$ – Tom Spilker May 1 '18 at 19:34

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