# Will Planet Earth ever be solid? **URL:** \ **Category:** Factual Questions\ **Created:** [November 16, 2019, 1:32am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520 "2019-11-16T01:32:40Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [November 16, 2019, 1:32am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/1 "2019-11-16T01:32:40Z")
The Earth has several layers: Inner core - solid metal. Outer core - liquid metal. Lower Mantle - solid. Upper mantle - plastic. Crust - solid. When originally formed it was a ball of very hot liquid. Since then it has been gradually cooling and solidifying. The inner core gradually increases in size, and the outer core shrinks. Given enough time, it will eventually be solid all through. But the planet won’t be around forever. The sun is predicted to become a red giant. Eventually it will expand beyond the orbit of Earth, and swallow up whatever is left of the planet. Question is, will the Earth have time to solidify before this happens? Will the Sun cooling have any effect on the Earth’s gradual solidifying? There is an alternative scenario where the planets recede from the Sun as it loses mass, so never get swallowed. But for this question lets assume that they remain in their current orbits. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 16, 2019, 2:33am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/2 "2019-11-16T02:33:32Z")
Well the planets are receding, so it’s not an “alternative scenario”. However, it’s uncertain if the Earth will recede far enough to avoid being engulfed. Every time I see someone do a study on this, they seem to contradict the last study. Anyway, what you’re really asking is Will the Earth solidify before the sun becomes a red giant? I believe the answer is no, it’s still be partially liquid. ---
**Author:** ![rbroome](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@rbroome](https://boards.straightdope.com/u/rbroome)\ **Post date:** [November 16, 2019, 2:36am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/3 "2019-11-16T02:36:33Z")
Can the earth ever completely solidify? I don’t know the triple point of iron, but the center of the earth may be under enough pressure to keep it liquid no matter what the temperature. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [November 16, 2019, 3:19am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/4 "2019-11-16T03:19:55Z")
> [@rbroome](#): > > Can the earth ever completely solidify? I don’t know the triple point of iron, but the center of the earth may be under enough pressure to keep it liquid no matter what the temperature. As the OP noted, the inner core is currently a solid. It is already at a temperature of over 5,000K. Would an expanded sun increase that significantly? It doesn’t seem likely since the sun’s surface is only about that temperature. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [November 16, 2019, 4:24am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/5 "2019-11-16T04:24:47Z")
The earth may stay hotter longer than you think. The heat inside the planet is not only due to “primordial heat” (the heat left over from the early formation days) but also due to on-going radioactive decay in the mantle. From Wikipedia article [Earth’s internal heat budget](https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget): > [@](#): > > Earth’s internal heat budget is fundamental to the thermal history of the Earth. The flow of heat from Earth’s interior to the surface is estimated at 47 ± 2 terawatts (TW) and comes from two main sources in roughly equal amounts: the radiogenic heat produced by the radioactive decay of isotopes in the mantle and crust, and the primordial heat left over from the formation of the Earth. ---
**Author:** ![RioRico](https://avatars.discourse-cdn.com/v4/letter/r/f04885/32.png) [@RioRico](https://boards.straightdope.com/u/RioRico)\ **Post date:** [November 16, 2019, 8:01am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/6 "2019-11-16T08:01:25Z")
A follow-up question: If Terra was flung to interstellar space on a path far from other suns, would it freeze solid, and if so, how long would that take? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [November 16, 2019, 8:21am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/7 "2019-11-16T08:21:48Z")
This second question has its own column. > **[If the sun goes out, how long till the earth freezes?](https://www.straightdope.com/columns/read/3293/if-the-sun-goes-out-how-long-till-the-earth-freezes/)** As to the first question, yes, the Earth will freeze solid one day, assuming it is not engulfed during the red giant phase or suffers a collision powerful enough to destroy it. The Sun will eventually turn into a black dwarf and the radioactivity in the planet’s rocks will eventually run out, reducing the temperature of the Earth to something near that of the microwave background. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [November 16, 2019, 8:32am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/8 "2019-11-16T08:32:06Z")
This article - the Timeline of the Far Future - describes some events that will affect the Earth’s temperature in the future. > **[Timeline of the far future](https://en.wikipedia.org/wiki/Timeline_of_the_far_future#Future_of_the_Earth,_the_Solar_System_and_the_universe)** > > While the future cannot be predicted with certainty, present understanding in various scientific fields allows for the prediction of some far-future events, if only in the broadest outline. These fields include astrophysics, which studies how planets and stars form, interact, and die; particle physics, which has revealed how matter behaves at the smallest scales; evolutionary biology, which studies how life evolves over time; plate tectonics, which shows how continents shift over millenn The ... For instance the Moon will probably collide with the Earth at around 150 billion years, and the Earth would hit the frozen Sun at 100 quintillion in the unlikely event it has not already been stripped away by external encounters. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [November 16, 2019, 11:44am UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/9 "2019-11-16T11:44:36Z")
If the sun would last forever, then the Earth’s core would solidify in roughly 91 billion years (according to an article from the National Geographic Society, I haven’t tried to do the math myself). The sun will not last forever, though. It will become a red giant and will completely destroy the Earth in roughly 5 billion years. So unless something comes along and flings the Earth outside of the Solar System, the Earth is doomed to die long before its core ever gets a chance to solidify. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [November 16, 2019, 1:08pm UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/10 "2019-11-16T13:08:45Z")
Thank you, e.c.g. that’s helpful and interesting. One question remains, will the cooling Sun affect Earth’s internal temperature? Does anyone know? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 16, 2019, 2:23pm UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/11 "2019-11-16T14:23:09Z")
The effect of the Sun’s heat is to keep the surface of the Earth at a temperature of around 300 K. The core of the Earth is at around 6000 K. So while the Sun does have an effect on the internal temperature of the Earth, it’s a very small one. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [November 16, 2019, 5:28pm UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/12 "2019-11-16T17:28:34Z")
> [@eburacum45](#): > > For instance the Moon will probably collide with the Earth at around 150 billion years, To clarify this, because it seemed wrong to me – the Moon’s orbit is slowly getting larger, and Earth’s day is getting longer, due to tidal effects. So the Moon is getting farther from the Earth. Without outside interference, the Moon would reach a (larger) stable orbit when the Earth becomes tidally locked to the Moon, and no collision would be possible. What that article is proposing is the outer atmosphere of the expanding red giant phase of the Sun would reach the Earth-Moon system and frictional drag caused by the Moon plowing through that atmosphere would slow it down and cause it to spiral into the Earth (before the Earth spirals into the Sun). As mentioned, there’s a lot of uncertainty about exactly how large the Sun will be in its red giant phase, so it’s not a sure thing that this will happen. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [November 16, 2019, 5:42pm UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/13 "2019-11-16T17:42:05Z")
> [@markn\_1](#): > > To clarify this, because it seemed wrong to me – the Moon’s orbit is slowly getting larger, and Earth’s day is getting longer, due to tidal effects. So the Moon is getting farther from the Earth. Without outside interference, the Moon would reach a (larger) stable orbit when the Earth becomes tidally locked to the Moon, and no collision would be possible. What that article is proposing is the outer atmosphere of the expanding red giant phase of the Sun would reach the Earth-Moon system and frictional drag caused by the Moon plowing through that atmosphere would slow it down and cause it to spiral into the Earth (before the Earth spirals into the Sun). As mentioned, there’s a lot of uncertainty about exactly how large the Sun will be in its red giant phase, so it’s not a sure thing that this will happen. Isn’t the moon set to fly out of Earth’s SoI? Then it would be a crapshoot what happens in their next encounter. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [November 16, 2019, 8:50pm UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/14 "2019-11-16T20:50:30Z")
> [@markn\_1](#): > > To clarify this, because it seemed wrong to me – the Moon’s orbit is slowly getting larger, and Earth’s day is getting longer, due to tidal effects. So the Moon is getting farther from the Earth. Without outside interference, the Moon would reach a (larger) stable orbit when the Earth becomes tidally locked to the Moon, and no collision would be possible. What that article is proposing is the outer atmosphere of the expanding red giant phase of the Sun would reach the Earth-Moon system and frictional drag caused by the Moon plowing through that atmosphere would slow it down and cause it to spiral into the Earth (before the Earth spirals into the Sun). As mentioned, there’s a lot of uncertainty about exactly how large the Sun will be in its red giant phase, so it’s not a sure thing that this will happen. I don’t think that is what they are saying. The red giant phase is quite short, and only five billion years in the future. I think the collision mentioned on the Wikipedia page will be caused by gravitational radiation. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [November 16, 2019, 9:08pm UTC](https://boards.straightdope.com/t/will-planet-earth-ever-be-solid/843520/15 "2019-11-16T21:08:26Z")
> [@eburacum45](#): > > I don’t think that is what they are saying. The red giant phase is quite short, and only five billion years in the future. I think the collision mentioned on the Wikipedia page will be caused by gravitational radiation. Ok, I looked up the citation given for the Wikipedia statement. Seems we’re both wrong (which means the Wikipedia statement should be clarified). This is what the [original source](https://www.forbes.com/sites/brucedorminey/2017/01/31/earth-and-moon-may-be-on-long-term-collision-course/#1ea7fc2e50d6) says: > [@](#): > > However, Barnes says eventually the Earth’s rotation will keep slowing until it’s the same as the Moon’s orbital period. At that point, the Moon will stop moving outward, he says. Assuming the Earth-Moon system has not been swallowed by a Red Giant Sun by that point, any remaining solar tides would soon sap energy from the Earth-Moon system. And the Moon would start creeping inwards, towards Earth. So it’s _solar_ tides that he’s claiming will cause the Moon’s orbit to decrease in size.