Ooh, ooh, this came up before! Nath has already explained, but there was a conversation about this structure in Chapter 4 starting here, just in case the connection / repetition is helpful to you or others 
I’d forgotten about this structure already so it was useful to have this reinforcement, thanks.
I’m already confused…
Page 189
Bottom panel
さあ 火星で
初めて迎える
地球の２倍長い
夏の始まりです
So, I get that the second box is loosely “it’s the beginning of a summer twice as long as that of earth”. I’m just not really sure how it links to the first box, which appears to be a relative clause modifying the second (?). Is it sort of like the first time she’s been greeted by summer?