kono wakusei ni ha seimei ga aru.

Because には is really two particles working together:

• に marks the location: on/in/at this planet
• は marks that location as the topic or adds contrast/emphasis

So この惑星には means something like:

• on this planet, ...
• as for this planet, ...
• at least on this planet, ...

This is very common with location expressions in Japanese.
With ある / いる, the basic pattern is often:

• place に thing が ある / いる

When は is added, the place is being highlighted as the topic:

• この惑星に生命がある = There is life on this planet.
• この惑星には生命がある = As for this planet, there is life on it / There is life on this planet.

The version with は can sound a little more like the speaker is focusing on this planet.

In this sentence, 生命 is the thing that exists, so it is marked by が.

With ある / いる, a very common structure is:

• place に thing が ある / いる

So here:

• この惑星には = on this planet
• 生命が = life
• ある = exists / there is

Using が is natural because it identifies what exists.

If you said 生命はある, that would change the nuance. It could sound more contrastive, like:

• Life does exist, though...
• As for life, there is some...

So が is the normal choice here.

Here, ある means to exist or to be present.

So 生命がある is literally:

• life exists

In natural English, that often becomes:

• There is life
• Life exists

Japanese often uses ある where English uses there is.

Because いる is used for people and animals, or other things treated as animate.
ある is used for inanimate things and abstract things.

生命 means life as a concept or phenomenon, not a living creature itself, so ある is used.

Compare:

• この惑星には生命がある。 = There is life on this planet.
• この惑星には動物がいる。 = There are animals on this planet.

So even though life relates to living things, the noun 生命 is treated grammatically as something that takes ある.

この means this and must directly modify a noun.

So:

• この惑星 = this planet

A common point of confusion is the difference between:

• この
  • noun = this ...
• これ = this one

So you can say:

• この惑星 = this planet

But not:

• これ惑星 ✘

If you want to use これ, it must stand alone:

• これは惑星です。 = This is a planet.

に does not always translate neatly as one single English preposition.

In this sentence, に marks the location where something exists. Depending on context, it may correspond to:

• in
• on
• at

So in この惑星に生命がある, に is best understood as a location marker, not as a direct one-word equivalent of English on.

That is why Japanese learners should focus on the pattern:

• place に thing が ある / いる

rather than trying to match に to only one English preposition.

Yes. You could say:

• この惑星に生命がある。

This is also grammatical and natural.

The difference is mainly nuance:

• この惑星に生命がある。 = There is life on this planet.
• この惑星には生命がある。 = On this planet, there is life / As for this planet, there is life.

The version with は gives more topical or contrastive focus to this planet. For example, it may suggest comparison with other planets.

Sometimes, yes.

は often adds a contrastive feeling, even if it is mild. So この惑星には生命がある can imply something like:

• There is life on this planet
  maybe unlike some others
• At least on this planet, there is life

However, the amount of contrast depends on context and tone. In many cases, it simply marks the topic naturally without strong contrast.

Japanese and English organize sentences differently.

This sentence follows a very common Japanese pattern:

• topic/location + subject + verb

So:

• この惑星には = on this planet / as for this planet
• 生命が = life
• ある = exists

Japanese verbs normally come at the end of the sentence, so ある appears last.

A very literal breakdown is:

• As for this planet, life exists.

That is why the Japanese word order feels different from English.

Not exactly.

• 生命 = life, especially in a scientific, biological, or abstract sense
• 命 = life, often meaning a life, one’s life, or life as something precious
• 生き物 = living thing / creature

In this sentence, 生命 is the best choice because the sentence is about the existence of life on a planet, which sounds scientific or factual.

Examples:

• この惑星には生命がある。 = There is life on this planet.
• 命は大切だ。 = Life is precious.
• この池には生き物がたくさんいる。 = There are many living creatures in this pond.

No. Normally, Japanese is written without spaces.

So the normal writing would be:

• この惑星には生命がある。

Spaces are often added only in beginner materials to make it easier to read:

• この　惑星　に　は　生命　が　ある。

That spaced version is for learning, not standard Japanese writing.

In some contexts, yes, but it is better to understand it literally first as there is / exists.

Japanese often expresses having with existence:

• A に B がある = A has B / There is B in A

So:

• この惑星には生命がある。

can be understood as:

• This planet has life
• There is life on this planet

Both are fine in English, but grammatically the Japanese is built from existence, not from a verb meaning to have.

Yes.

Different particles change the focus and nuance.

For example:

• この惑星には生命がある。
  Focuses on this planet as topic/location.

• この惑星に生命はある。
  Puts contrast on life. This could sound like: As for life, this planet does have it.

• この惑星に生命がある。
  A more neutral statement of existence.

So the basic meaning may stay similar, but the emphasis changes depending on which particle you choose.